Metalloid

A metalloid is a type of chemical element which has properties in between, or that are a mixture of, those of metals and nonmetals. There is neither a standard definition of a metalloid nor complete agreement on the elements appropriately classified as such. Despite the lack of specificity, the term remains in use in the literature of chemistry.

Elements recognized as metalloids
	13	14	15	16	17
2	B Boron	C Carbon	N Nitrogen	O Oxygen	F Fluorine
3	Al Aluminium	Si Silicon	P Phosphorus	S Sulfur	Cl Chlorine
4	Ga Gallium	Ge Germanium	As Arsenic	Se Selenium	Br Bromine
5	In Indium	Sn Tin	Sb Antimony	Te Tellurium	I Iodine
6	Tl Thallium	Pb Lead	Bi Bismuth	Po Polonium	At Astatine
Commonly recognized (93%): B, Si, Ge, As, Sb, Te   Irregularly recognized (44%): Po, At   Less commonly recognized (24%): Se   Rarely recognized (9%): C, Al   Arbitrary metal-nonmetal dividing line: between Be and B, Al and Si, Ge and As, Sb and Te, Po and At
Recognition status, as metalloids, of some elements in the p-block of the periodic table. Percentages are median appearance frequencies in the lists of metalloids.[n 1] The staircase-shaped line is a typical example of the arbitrary metal–nonmetal dividing line found on some periodic tables.

The six commonly recognised metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. Five elements are less frequently so classified: carbon, aluminium, selenium, polonium, and astatine. On a standard periodic table, all eleven elements are located in a diagonal region of the p-block extending from boron at the upper left to astatine at lower right. Some periodic tables include a dividing line between metals and nonmetals and the metalloids may be found close to this line.

Typical metalloids have a metallic appearance, but they are brittle and only fair conductors of electricity. Chemically, they behave mostly as nonmetals. They can form alloys with metals. Most of their other physical properties and chemical properties are intermediate in nature. Metalloids are usually too brittle to have any structural uses. They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.

The electrical properties of silicon and germanium enabled the establishment of the semiconductor industry in the 1950s and the development of solid-state electronics from the early 1960s.[1]

The term metalloid originally referred to nonmetals. Its more recent meaning, as a category of elements with intermediate or hybrid properties, became widespread in 1940–1960. Metalloids are sometimes called semimetals, a practice that has been discouraged,[2] as the term semimetal has a different meaning in physics than in chemistry. In physics, it specifically refers to the electronic band structure of a substance.

Definitions

See also: Lists of metalloids

Judgement-based

A metalloid is an element that possesses properties of both metals and non metals, and which is therefore hard to classify as either a metal or a nonmetal. This is a generic definition that draws on metalloid attributes consistently cited in the literature.[n 2] Difficulty of categorisation is a key attribute. Most elements have a mixture of metallic and nonmetallic properties,[9] and can be classified according to which set of properties is more pronounced.[10][n 3] Only the elements at or near the margins, lacking a sufficiently clear preponderance of either metallic or nonmetallic properties, are classified as metalloids.[14]

Boron, silicon, germanium, arsenic, antimony, and tellurium are commonly recognised as metalloids.[15][n 4] Depending on the author, one or more from selenium, polonium, or astatine are sometimes added to the list.[17] Boron sometimes is excluded, by itself, or with silicon.[18] Sometimes tellurium is not regarded as a metalloid.[19] The inclusion of antimony, polonium, and astatine as metalloids has been questioned.[20]

Other elements are occasionally classified as metalloids. These elements include[21] hydrogen,[22] beryllium,[23] nitrogen,[24] phosphorus,[25] sulfur,[26] zinc,[27] gallium,[28] tin, iodine,[29] lead,[30] bismuth,[19] and radon.[31] The term metalloid has also been used for elements that exhibit metallic lustre and electrical conductivity, and that are amphoteric, such as arsenic, antimony, vanadium, chromium, molybdenum, tungsten, tin, lead, and aluminium.[32] The p-block metals,[33] and nonmetals (such as carbon or nitrogen) that can form alloys with metals[34] or modify their properties[35] have also occasionally been considered as metalloids.

Criteria-based

Element	IE (kcal/mol)	IE (kJ/mol)	EN	Band structure
Boron	191	801	2.04	semiconductor
Silicon	188	787	1.90	semiconductor
Germanium	182	762	2.01	semiconductor
Arsenic	226	944	2.18	semimetal
Antimony	199	831	2.05	semimetal
Tellurium	208	869	2.10	semiconductor
average	199	832	2.05
The elements commonly recognised as metalloids, and their ionization energies (IE);[36] electronegativities (EN, revised Pauling scale); and electronic band structures[37] (most thermodynamically-stable forms under ambient conditions).

No widely accepted definition of a metalloid exists, nor any division of the periodic table into metals, metalloids, and nonmetals;[38] Hawkes[39] questioned the feasibility of establishing a specific definition, noting that anomalies can be found in several attempted constructs. Classifying an element as a metalloid has been described by Sharp[40] as "arbitrary".

The number and identities of metalloids depend on what classification criteria are used. Emsley[41] recognised four metalloids (germanium, arsenic, antimony, and tellurium); James et al.[42] listed twelve (Emsley's plus boron, carbon, silicon, selenium, bismuth, polonium, moscovium, and livermorium). On average, seven elements are included in such lists; individual classification arrangements tend to share common ground and vary in the ill-defined[43] margins.[n 5][n 6]

A single quantitative criterion such as electronegativity is commonly used,[46] metalloids having electronegativity values from 1.8 or 1.9 to 2.2.[47] Further examples include packing efficiency (the fraction of volume in a crystal structure occupied by atoms) and the Goldhammer-Herzfeld criterion ratio.[48] The commonly recognised metalloids have packing efficiencies of between 34% and 41%.[n 7] The Goldhammer-Herzfeld ratio, roughly equal to the cube of the atomic radius divided by the molar volume,[56][n 8] is a simple measure of how metallic an element is, the recognised metalloids having ratios from around 0.85 to 1.1 and averaging 1.0.[58][n 9] Other authors have relied on, for example, atomic conductance[n 10][62] or bulk coordination number.[63]

Jones, writing on the role of classification in science, observed that "[classes] are usually defined by more than two attributes".[64] Masterton and Slowinski[65] used three criteria to describe the six elements commonly recognised as metalloids: metalloids have ionization energies around 200 kcal/mol (837 kJ/mol) and electronegativity values close to 2.0. They also said that metalloids are typically semiconductors, though antimony and arsenic (semimetals from a physics perspective) have electrical conductivities approaching those of metals. Selenium and polonium are suspected as not in this scheme, while astatine's status is uncertain.[n 11]

In this context, Vernon proposed that a metalloid is a chemical element that, in its standard state, has (a) the electronic band structure band structure of a semiconductor or a semimetal; and (b) an intermediate first ionization potential "(say 750−1,000 kJ/mol)"; and (c) an intermediate electronegativity (1.9−2.2).[68]

Periodic table territory

Location

Distribution and recognition status of elements classified as metalloids
	1	2		12	13	14	15	16	17	18
	H									He
	Li	Be			B	C	N	O	F	Ne
	Na	Mg			Al	Si	P	S	Cl	Ar
	K	Ca		Zn	Ga	Ge	As	Se	Br	Kr
	Rb	Sr		Cd	In	Sn	Sb	Te	I	Xe
	Cs	Ba		Hg	Tl	Pb	Bi	Po	At	Rn
	Fr	Ra		Cn	Nh	Fl	Mc	Lv	Ts	Og
	Commonly (93%) to rarely (9%) recognised as a metalloid: B, C, Al, Si, Ge, As, Se, Sb, Te, Po, At   Very rarely (1–5%): H, Be, P, S, Ga, Sn, I, Pb, Bi, Fl, Mc, Lv, Ts   Sporadically: N, Zn, Rn   Metal–nonmetal dividing line: between H and Li, Be and B, Al and Si, Ge and As, Sb and Te, Po and At, and Ts and Og
Periodic table extract showing groups 1–2 and 12–18, and a dividing line between metals and nonmetals. Percentages are median appearance frequencies in the list of metalloid lists. Sporadically recognised elements show that the metalloid net is sometimes cast very widely; although they do not appear in the list of metalloid lists, isolated references to their designation as metalloids can be found in the literature (as cited in this article).

Metalloids lie on either side of the dividing line between metals and nonmetals. This can be found, in varying configurations, on some periodic tables. Elements to the lower left of the line generally display increasing metallic behaviour; elements to the upper right display increasing nonmetallic behaviour.[69] When presented as a regular stairstep, elements with the highest critical temperature for their groups (Li, Be, Al, Ge, Sb, Po) lie just below the line.[70]

The diagonal positioning of the metalloids represents an exception to the observation that elements with similar properties tend to occur in vertical groups.[71] A related effect can be seen in other diagonal similarities between some elements and their lower right neighbours, specifically lithium-magnesium, beryllium-aluminium, and boron-silicon. Rayner-Canham[72] has argued that these similarities extend to carbon-phosphorus, nitrogen-sulfur, and into three d-block series.

This exception arises due to competing horizontal and vertical trends in the nuclear charge. Going along a period, the nuclear charge increases with atomic number as do the number of electrons. The additional pull on outer electrons as nuclear charge increases generally outweighs the screening effect of having more electrons. With some irregularities, atoms therefore become smaller, ionization energy increases, and there is a gradual change in character, across a period, from strongly metallic, to weakly metallic, to weakly nonmetallic, to strongly nonmetallic elements.[73] Going down a main group, the effect of increasing nuclear charge is generally outweighed by the effect of additional electrons being further away from the nucleus. Atoms generally become larger, ionization energy falls, and metallic character increases.[74] The net effect is that the location of the metal–nonmetal transition zone shifts to the right in going down a group,[71] and analogous diagonal similarities are seen elsewhere in the periodic table, as noted.[75]

Alternative treatments

Depictions of metalloids vary according to the author. Some do not classify elements bordering the metal–nonmetal dividing line as metalloids, noting that a binary classification can facilitate the establishment of rules for determining bond types between metals and nonmetals.[76] Metalloids are variously grouped with metals,[77] regarded as nonmetals[78] or treated as a sub-category of nonmetals.[79][n 12] Other authors have suggested that classifying some elements as metalloids "emphasizes that properties change gradually rather than abruptly as one moves across or down the periodic table".[81] Some periodic tables distinguish elements that are metalloids and display no formal dividing line between metals and nonmetals. Metalloids are shown as occurring in a diagonal band[82] or diffuse region.[83]

Properties

Metalloids usually look like metals but behave largely like nonmetals. Physically, they are shiny, brittle solids with intermediate to relatively good electrical conductivity and the electronic band structure of a semimetal or semiconductor. Chemically, they mostly behave as (weak) nonmetals, have intermediate ionization energies and electronegativity values, and amphoteric or weakly acidic oxides. They can form alloys with metals. Most of their other physical and chemical properties are intermediate in nature.

Compared to metals and nonmetals

Characteristic properties of metals, metalloids, and nonmetals are summarized in the table.[84] Physical properties are listed in order of ease of determination; chemical properties run from general to specific, and then to descriptive.

Properties of metals, metalloids, and nonmetals

Physical property	Metals	Metalloids	Nonmetals
Form	solid; a few liquid at or near room temperature (Ga, Hg, Rb, Cs, Fr)[85][n 13]	solid[87]	majority gaseous[88]
Appearance	lustrous (at least when freshly fractured)	lustrous[87]	several colourless; others coloured, or metallic grey to black
Elasticity	typically elastic, ductile, malleable (when solid)	brittle[89]	brittle, if solid
Electrical conductivity	good to high[n 14]	intermediate[91] to good[n 15]	poor to good[n 16]
Band structure	metallic (Bi = semimetallic)	are semiconductors or, if not (As, Sb = semimetallic), exist in semiconducting forms[95]	semiconductor or insulator[96]
Chemical property	Metals	Metalloids	Nonmetals
General chemical behaviour	metallic	nonmetallic[97]	nonmetallic
Ionization energy	relatively low	intermediate ionization energies,[98] usually falling between those of metals and nonmetals[99]	relatively high
Electronegativity	usually low	have electronegativity values close to 2[100] (revised Pauling scale) or within the range of 1.9–2.2 (Allen scale)[16][n 17]	high
When mixed with metals	give alloys	can form alloys[103]	ionic or interstitial compounds formed
Oxides	lower oxides basic; higher oxides increasingly acidic	amphoteric or weakly acidic[104]	acidic

The above table reflects the hybrid nature of metalloids. The properties of form, appearance, and behaviour when mixed with metals are more like metals. Elasticity and general chemical behaviour are more like nonmetals. Electrical conductivity, band structure, ionization energy, electronegativity, and oxides are intermediate between the two.

Common applications

The focus of this section is on the recognised metalloids. Elements less often recognised as metalloids are ordinarily classified as either metals or nonmetals; some of these are included here for comparative purposes.

Metalloids are too brittle to have any structural uses in their pure forms.[105] They and their compounds are used as (or in) alloying components, biological agents (toxicological, nutritional, and medicinal), catalysts, flame retardants, glasses (oxide and metallic), optical storage media and optoelectronics, pyrotechnics, semiconductors, and electronics.[n 18]

Alloys

Copper-germanium alloy pellets, likely ~84% Cu; 16% Ge.[107] When combined with silver the result is a tarnish resistant sterling silver. Also shown are two silver pellets.

Writing early in the history of intermetallic compounds, the British metallurgist Cecil Desch observed that "certain non-metallic elements are capable of forming compounds of distinctly metallic character with metals, and these elements may therefore enter into the composition of alloys". He associated silicon, arsenic, and tellurium, in particular, with the alloy-forming elements.[108] Phillips and Williams[109] suggested that compounds of silicon, germanium, arsenic, and antimony with B metals, "are probably best classed as alloys".

Among the lighter metalloids, alloys with transition metals are well-represented. Boron can form intermetallic compounds and alloys with such metals of the composition M_nB, if n > 2.[110] Ferroboron (15% boron) is used to introduce boron into steel; nickel-boron alloys are ingredients in welding alloys and case hardening compositions for the engineering industry. Alloys of silicon with iron and with aluminium are widely used by the steel and automotive industries, respectively. Germanium forms many alloys, most importantly with the coinage metals.[111]

The heavier metalloids continue the theme. Arsenic can form alloys with metals, including platinum and copper;[112] it is also added to copper and its alloys to improve corrosion resistance[113] and appears to confer the same benefit when added to magnesium.[114] Antimony is well known as an alloy-former, including with the coinage metals. Its alloys include pewter (a tin alloy with up to 20% antimony) and type metal (a lead alloy with up to 25% antimony).[115] Tellurium readily alloys with iron, as ferrotellurium (50–58% tellurium), and with copper, in the form of copper tellurium (40–50% tellurium).[116] Ferrotellurium is used as a stabilizer for carbon in steel casting.[117] Of the non-metallic elements less often recognised as metalloids, selenium—in the form of ferroselenium (50–58% selenium)—is used to improve the machinability of stainless steels.[118]

Biological agents

Arsenic trioxide or white arsenic, one of the most toxic and prevalent forms of arsenic. The antileukaemic properties of white arsenic were first reported in 1878.[119]

All six of the elements commonly recognised as metalloids have toxic, dietary or medicinal properties.[120] Arsenic and antimony compounds are especially toxic; boron, silicon, and possibly arsenic, are essential trace elements. Boron, silicon, arsenic, and antimony have medical applications, and germanium and tellurium are thought to have potential.

Boron is used in insecticides[121] and herbicides.[122] It is an essential trace element.[123] As boric acid, it has antiseptic, antifungal, and antiviral properties.[124]

Silicon is present in silatrane, a highly toxic rodenticide.[125] Long-term inhalation of silica dust causes silicosis, a fatal disease of the lungs. Silicon is an essential trace element.[123] Silicone gel can be applied to badly burned patients to reduce scarring.[126]

Salts of germanium are potentially harmful to humans and animals if ingested on a prolonged basis.[127] There is interest in the pharmacological actions of germanium compounds but no licensed medicine as yet.[128]

Arsenic is notoriously poisonous and may also be an essential element in ultratrace amounts.[129] During World War I, both sides used "arsenic-based sneezing and vomiting agents…to force enemy soldiers to remove their gas masks before firing mustard or phosgene at them in a second salvo."[130] It has been used as a pharmaceutical agent since antiquity, including for the treatment of syphilis before the development of antibiotics.[131] Arsenic is also a component of melarsoprol, a medicinal drug used in the treatment of human African trypanosomiasis or sleeping sickness. In 2003, arsenic trioxide (under the trade name Trisenox) was re-introduced for the treatment of acute promyelocytic leukaemia, a cancer of the blood and bone marrow.[131] Arsenic in drinking water, which causes lung and bladder cancer, has been associated with a reduction in breast cancer mortality rates.[132]

Metallic antimony is relatively non-toxic, but most antimony compounds are poisonous.[133] Two antimony compounds, sodium stibogluconate and stibophen, are used as antiparasitical drugs.[134]

Elemental tellurium is not considered particularly toxic; two grams of sodium tellurate, if administered, can be lethal.[135] People exposed to small amounts of airborne tellurium exude a foul and persistent garlic-like odour.[136] Tellurium dioxide has been used to treat seborrhoeic dermatitis; other tellurium compounds were used as antimicrobial agents before the development of antibiotics.[137] In the future, such compounds may need to be substituted for antibiotics that have become ineffective due to bacterial resistance.[138]

Of the elements less often recognised as metalloids, beryllium and lead are noted for their toxicity; lead arsenate has been extensively used as an insecticide.[139] Sulfur is one of the oldest of the fungicides and pesticides. Phosphorus, sulfur, zinc, selenium, and iodine are essential nutrients, and aluminium, tin, and lead may be.[129] Sulfur, gallium, selenium, iodine, and bismuth have medicinal applications. Sulfur is a constituent of sulfonamide drugs, still widely used for conditions such as acne and urinary tract infections.[140] Gallium nitrate is used to treat the side effects of cancer;[141] gallium citrate, a radiopharmaceutical, facilitates imaging of inflamed body areas.[142] Selenium sulfide is used in medicinal shampoos and to treat skin infections such as tinea versicolor.[143] Iodine is used as a disinfectant in various forms. Bismuth is an ingredient in some antibacterials.[144]

Catalysts

Boron trifluoride and trichloride are used as catalysts in organic synthesis and electronics; the tribromide is used in the manufacture of diborane.[145] Non-toxic boron ligands could replace toxic phosphorus ligands in some transition metal catalysts.[146] Silica sulfuric acid (SiO₂OSO₃H) is used in organic reactions.[147] Germanium dioxide is sometimes used as a catalyst in the production of PET plastic for containers;[148] cheaper antimony compounds, such as the trioxide or triacetate, are more commonly employed for the same purpose[149] despite concerns about antimony contamination of food and drinks.[150] Arsenic trioxide has been used in the production of natural gas, to boost the removal of carbon dioxide, as have selenous acid and tellurous acid.[151] Selenium acts as a catalyst in some microorganisms.[152] Tellurium, its dioxide, and its tetrachloride are strong catalysts for air oxidation of carbon above 500 °C.[153] Graphite oxide can be used as a catalyst in the synthesis of imines and their derivatives.[154] Activated carbon and alumina have been used as catalysts for the removal of sulfur contaminants from natural gas.[155] Titanium doped aluminium has been identified as a substitute for expensive noble metal catalysts used in the production of industrial chemicals.[156]

Flame retardants

Compounds of boron, silicon, arsenic, and antimony have been used as flame retardants. Boron, in the form of borax, has been used as a textile flame retardant since at least the 18th century.[157] Silicon compounds such as silicones, silanes, silsesquioxane, silica, and silicates, some of which were developed as alternatives to more toxic halogenated products, can considerably improve the flame retardancy of plastic materials.[158] Arsenic compounds such as sodium arsenite or sodium arsenate are effective flame retardants for wood but have been less frequently used due to their toxicity.[159] Antimony trioxide is a flame retardant.[160] Aluminium hydroxide has been used as a wood-fibre, rubber, plastic, and textile flame retardant since the 1890s.[161] Apart from aluminium hydroxide, use of phosphorus based flame-retardants—in the form of, for example, organophosphates—now exceeds that of any of the other main retardant types. These employ boron, antimony, or halogenated hydrocarbon compounds.[162]

Glass formation

Optical fibres, usually made of pure silicon dioxide glass, with additives such as boron trioxide or germanium dioxide for increased sensitivity

The oxides B₂O₃, SiO₂, GeO₂, As₂O₃, and Sb₂O₃ readily form glasses. TeO₂ forms a glass but this requires a "heroic quench rate"[163] or the addition of an impurity; otherwise the crystalline form results.[163] These compounds are used in chemical, domestic, and industrial glassware[164] and optics.[165] Boron trioxide is used as a glass fibre additive,[166] and is also a component of borosilicate glass, widely used for laboratory glassware and domestic ovenware for its low thermal expansion.[167] Most ordinary glassware is made from silicon dioxide.[168] Germanium dioxide is used as a glass fibre additive, as well as in infrared optical systems.[169] Arsenic trioxide is used in the glass industry as a decolourizing and fining agent (for the removal of bubbles),[170] as is antimony trioxide.[171] Tellurium dioxide finds application in laser and nonlinear optics.[172]

Amorphous metallic glasses are generally most easily prepared if one of the components is a metalloid or "near metalloid" such as boron, carbon, silicon, phosphorus or germanium.[173][n 19] Aside from thin films deposited at very low temperatures, the first known metallic glass was an alloy of composition Au₇₅Si₂₅ reported in 1960.[175] A metallic glass having a strength and toughness not previously seen, of composition Pd_82.5P₆Si_9.5Ge₂, was reported in 2011.[176]

Phosphorus, selenium, and lead, which are less often recognised as metalloids, are also used in glasses. Phosphate glass has a substrate of phosphorus pentoxide (P₂O₅), rather than the silica (SiO₂) of conventional silicate glasses. It is used, for example, to make sodium lamps.[177] Selenium compounds can be used both as decolourising agents and to add a red colour to glass.[178] Decorative glassware made of traditional lead glass contains at least 30% lead(II) oxide (PbO); lead glass used for radiation shielding may have up to 65% PbO.[179] Lead-based glasses have also been extensively used in electronic components, enamelling, sealing and glazing materials, and solar cells. Bismuth based oxide glasses have emerged as a less toxic replacement for lead in many of these applications.[180]

Optical storage and optoelectronics

Varying compositions of GeSbTe ("GST alloys") and Ag- and In- doped Sb₂Te ("AIST alloys"), being examples of phase-change materials, are widely used in rewritable optical discs and phase-change memory devices. By applying heat, they can be switched between amorphous (glassy) and crystalline states. The change in optical and electrical properties can be used for information storage purposes.[181] Future applications for GeSbTe may include, "ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent 'smart' glasses, 'smart' contact lenses, and artificial retina devices."[182]

Pyrotechnics

Archaic blue light signal, fuelled by a mixture of sodium nitrate, sulfur, and (red) arsenic trisulfide[183]

The recognised metalloids have either pyrotechnic applications or associated properties. Boron and silicon are commonly encountered;[184] they act somewhat like metal fuels.[185] Boron is used in pyrotechnic initiator compositions (for igniting other hard-to-start compositions), and in delay compositions that burn at a constant rate.[186] Boron carbide has been identified as a possible replacement for more toxic barium or hexachloroethane mixtures in smoke munitions, signal flares, and fireworks.[187] Silicon, like boron, is a component of initiator and delay mixtures.[186] Doped germanium can act as a variable speed thermite fuel.[n 20] Arsenic trisulfide As₂S₃ was used in old naval signal lights; in fireworks to make white stars;[189] in yellow smoke screen mixtures; and in initiator compositions.[190] Antimony trisulfide Sb₂S₃ is found in white-light fireworks and in flash and sound mixtures.[191] Tellurium has been used in delay mixtures and in blasting cap initiator compositions.[192]

Carbon, aluminium, phosphorus, and selenium continue the theme. Carbon, in black powder, is a constituent of fireworks rocket propellants, bursting charges, and effects mixtures, and military delay fuses and igniters.[193][n 21] Aluminium is a common pyrotechnic ingredient,[184] and is widely employed for its capacity to generate light and heat,[195] including in thermite mixtures.[196] Phosphorus can be found in smoke and incendiary munitions, paper caps used in toy guns, and party poppers.[197] Selenium has been used in the same way as tellurium.[192]

Semiconductors and electronics

Semiconductor-based electronic components. From left to right: a transistor, an integrated circuit, and an LED. The elements commonly recognised as metalloids find widespread use in such devices, as elemental or compound semiconductor constituents (Si, Ge or GaAs, for example) or as doping agents (B, Sb, Te, for example).

All the elements commonly recognised as metalloids (or their compounds) have been used in the semiconductor or solid-state electronic industries.[198]

Some properties of boron have limited its use as a semiconductor. It has a high melting point, single crystals are relatively hard to obtain, and introducing and retaining controlled impurities is difficult.[199]

Silicon is the leading commercial semiconductor; it forms the basis of modern electronics (including standard solar cells)[200] and information and communication technologies.[201] This was despite the study of semiconductors, early in the 20th century, having been regarded as the "physics of dirt" and not deserving of close attention.[202]

Germanium has largely been replaced by silicon in semiconducting devices, being cheaper, more resilient at higher operating temperatures, and easier to work during the microelectronic fabrication process.[107] Germanium is still a constituent of semiconducting silicon-germanium "alloys" and these have been growing in use, particularly for wireless communication devices; such alloys exploit the higher carrier mobility of germanium.[107] The synthesis of gram-scale quantities of semiconducting germanane was reported in 2013. This consists of one-atom thick sheets of hydrogen-terminated germanium atoms, analogous to graphane. It conducts electrons more than ten times faster than silicon and five times faster than germanium, and is thought to have potential for optoelectronic and sensing applications.[203] The development of a germanium-wire based anode that more than doubles the capacity of lithium-ion batteries was reported in 2014.[204] In the same year, Lee et al. reported that defect-free crystals of graphene large enough to have electronic uses could be grown on, and removed from, a germanium substrate.[205]

Arsenic and antimony are not semiconductors in their standard states. Both form type III-V semiconductors (such as GaAs, AlSb or GaInAsSb) in which the average number of valence electrons per atom is the same as that of Group 14 elements. These compounds are preferred for some special applications.[206] Antimony nanocrystals may enable lithium-ion batteries to be replaced by more powerful sodium ion batteries.[207]

Tellurium, which is a semiconductor in its standard state, is used mainly as a component in type II/VI semiconducting-chalcogenides; these have applications in electro-optics and electronics.[208] Cadmium telluride (CdTe) is used in solar modules for its high conversion efficiency, low manufacturing costs, and large band gap of 1.44 eV, letting it absorb a wide range of wavelengths.[200] Bismuth telluride (Bi₂Te₃), alloyed with selenium and antimony, is a component of thermoelectric devices used for refrigeration or portable power generation.[209]

Five metalloids—boron, silicon, germanium, arsenic, and antimony—can be found in cell phones (along with at least 39 other metals and nonmetals).[210] Tellurium is expected to find such use.[211] Of the less often recognised metalloids, phosphorus, gallium (in particular) and selenium have semiconductor applications. Phosphorus is used in trace amounts as a dopant for n-type semiconductors.[212] The commercial use of gallium compounds is dominated by semiconductor applications—in integrated circuits, cell phones, laser diodes, light-emitting diodes, photodetectors, and solar cells.[213] Selenium is used in the production of solar cells[214] and in high-energy surge protectors.[215]

Boron, silicon, germanium, antimony, and tellurium,[216] as well as heavier metals and metalloids such as Sm, Hg, Tl, Pb, Bi, and Se,[217] can be found in topological insulators. These are alloys[218] or compounds which, at ultracold temperatures or room temperature (depending on their composition), are metallic conductors on their surfaces but insulators through their interiors.[219] Cadmium arsenide Cd₃As₂, at about 1 K, is a Dirac-semimetal—a bulk electronic analogue of graphene—in which electrons travel effectively as massless particles.[220] These two classes of material are thought to have potential quantum computing applications.[221]

Nomenclature and history

Derivation and other names

The word metalloid comes from the Latin metallum ("metal") and the Greek oeides ("resembling in form or appearance").[222] Several names are sometimes used synonymously although some of these have other meanings that are not necessarily interchangeable: amphoteric element,[223] boundary element,[224] half-metal,[225] half-way element,[226] near metal,[227] meta-metal,[228] semiconductor,[229] semimetal[230] and submetal.[231] "Amphoteric element" is sometimes used more broadly to include transition metals capable of forming oxyanions, such as chromium and manganese.[232] "Half-metal" is used in physics to refer to a compound (such as chromium dioxide) or alloy that can act as a conductor and an insulator. "Meta-metal" is sometimes used instead to refer to certain metals (Be, Zn, Cd, Hg, In, Tl, β-Sn, Pb) located just to the left of the metalloids on standard periodic tables.[225] These metals are mostly diamagnetic[233] and tend to have distorted crystalline structures, electrical conductivity values at the lower end of those of metals, and amphoteric (weakly basic) oxides.[234] "Semimetal" sometimes refers, loosely or explicitly, to metals with incomplete metallic character in crystalline structure, electrical conductivity or electronic structure. Examples include gallium,[235] ytterbium,[236] bismuth[237] and neptunium.[238] The names amphoteric element and semiconductor are problematic as some elements referred to as metalloids do not show marked amphoteric behaviour (bismuth, for example)[239] or semiconductivity (polonium)[240] in their most stable forms.

Origin and usage

Main article: Origin and use of the term metalloid

The origin and usage of the term metalloid is convoluted. Its origin lies in attempts, dating from antiquity, to describe metals and to distinguish between typical and less typical forms. It was first applied in the early 19th century to metals that floated on water (sodium and potassium), and then more popularly to nonmetals. Earlier usage in mineralogy, to describe a mineral having a metallic appearance, can be sourced to as early as 1800.[241] Since the mid-20th century it has been used to refer to intermediate or borderline chemical elements.[242][n 22] The International Union of Pure and Applied Chemistry (IUPAC) previously recommended abandoning the term metalloid, and suggested using the term semimetal instead.[244] Use of this latter term has more recently been discouraged by Atkins et al.[2] as it has a different meaning in physics—one that more specifically refers to the electronic band structure of a substance rather than the overall classification of an element. The most recent IUPAC publications on nomenclature and terminology do not include any recommendations on the usage of the terms metalloid or semimetal.[245]

Elements commonly recognised as metalloids

Properties noted in this section refer to the elements in their most thermodynamically stable forms under ambient conditions.

Boron

Main article: Boron

Boron, shown here in the form of its β-rhombohedral phase (its most thermodynamically stable allotrope)[246]

Pure boron is a shiny, silver-grey crystalline solid.[247] It is less dense than aluminium (2.34 vs. 2.70 g/cm³), and is hard and brittle. It is barely reactive under normal conditions, except for attack by fluorine,[248] and has a melting point of 2076 °C (cf. steel ~1370 °C).[249] Boron is a semiconductor;[250] its room temperature electrical conductivity is 1.5 × 10⁻⁶ S•cm⁻¹[251] (about 200 times less than that of tap water)[252] and it has a band gap of about 1.56 eV.[253][n 23] Mendeleev commented that, "Boron appears in a free state in several forms which are intermediate between the metals and the nonmmetals."[255]

The structural chemistry of boron is dominated by its small atomic size, and relatively high ionization energy. With only three valence electrons per boron atom, simple covalent bonding cannot fulfil the octet rule.[256] Metallic bonding is the usual result among the heavier congenors of boron but this generally requires low ionization energies.[257] Instead, because of its small size and high ionization energies, the basic structural unit of boron (and nearly all of its allotropes)[n 24] is the icosahedral B₁₂ cluster. Of the 36 electrons associated with 12 boron atoms, 26 reside in 13 delocalized molecular orbitals; the other 10 electrons are used to form two- and three-centre covalent bonds between icosahedra.[259] The same motif can be seen, as are deltahedral variants or fragments, in metal borides and hydride derivatives, and in some halides.[260]

The bonding in boron has been described as being characteristic of behaviour intermediate between metals and nonmetallic covalent network solids (such as diamond).[261] The energy required to transform B, C, N, Si, and P from nonmetallic to metallic states has been estimated as 30, 100, 240, 33, and 50 kJ/mol, respectively. This indicates the proximity of boron to the metal-nonmetal borderline.[262]

Most of the chemistry of boron is nonmetallic in nature.[262] Unlike its heavier congeners, it is not known to form a simple B³⁺ or hydrated [B(H₂O)₄]³⁺ cation.[263] The small size of the boron atom enables the preparation of many interstitial alloy-type borides.[264] Analogies between boron and transition metals have been noted in the formation of complexes,[265] and adducts (for example, BH₃ + CO →BH₃CO and, similarly, Fe(CO)₄ + CO →Fe(CO)₅),[n 25] as well as in the geometric and electronic structures of cluster species such as [B₆H₆]²⁻ and [Ru₆(CO)₁₈]²⁻.[267][n 26] The aqueous chemistry of boron is characterised by the formation of many different polyborate anions.[269] Given its high charge-to-size ratio, boron bonds covalently in nearly all of its compounds;[270] the exceptions are the borides as these include, depending on their composition, covalent, ionic, and metallic bonding components.[271][n 27] Simple binary compounds, such as boron trichloride are Lewis acids as the formation of three covalent bonds leaves a hole in the octet which can be filled by an electron-pair donated by a Lewis base.[256] Boron has a strong affinity for oxygen and a duly extensive borate chemistry.[264] The oxide B₂O₃ is polymeric in structure,[274] weakly acidic,[275][n 28] and a glass former.[281] Organometallic compounds of boron[n 29] have been known since the 19th century (see organoboron chemistry).[283]

Silicon

Main article: Silicon

Silicon has a blue-grey metallic lustre.

Silicon is a crystalline solid with a blue-grey metallic lustre.[284] Like boron, it is less dense (at 2.33 g/cm³) than aluminium, and is hard and brittle.[285] It is a relatively unreactive element.[284] According to Rochow,[286] the massive crystalline form (especially if pure) is "remarkably inert to all acids, including hydrofluoric".[n 30] Less pure silicon, and the powdered form, are variously susceptible to attack by strong or heated acids, as well as by steam and fluorine.[290] Silicon dissolves in hot aqueous alkalis with the evolution of hydrogen, as do metals[291] such as beryllium, aluminium, zinc, gallium or indium.[292] It melts at 1414 °C. Silicon is a semiconductor with an electrical conductivity of 10⁻⁴ S•cm⁻¹[293] and a band gap of about 1.11 eV.[287] When it melts, silicon becomes a reasonable metal[294] with an electrical conductivity of 1.0–1.3 × 10⁴ S•cm⁻¹, similar to that of liquid mercury.[295]

The chemistry of silicon is generally nonmetallic (covalent) in nature.[296] It is not known to form a cation.[297][n 31] Silicon can form alloys with metals such as iron and copper.[298] It shows fewer tendencies to anionic behaviour than ordinary nonmetals.[299] Its solution chemistry is characterised by the formation of oxyanions.[300] The high strength of the silicon-oxygen bond dominates the chemical behaviour of silicon.[301] Polymeric silicates, built up by tetrahedral SiO₄ units sharing their oxygen atoms, are the most abundant and important compounds of silicon.[302] The polymeric borates, comprising linked trigonal and tetrahedral BO₃ or BO₄ units, are built on similar structural principles.[303] The oxide SiO₂ is polymeric in structure,[274] weakly acidic,[304][n 32] and a glass former.[281] Traditional organometallic chemistry includes the carbon compounds of silicon (see organosilicon).[308]

Germanium

Main article: Germanium

Germanium is sometimes described as a metal

Germanium is a shiny grey-white solid.[309] It has a density of 5.323 g/cm³ and is hard and brittle.[310] It is mostly unreactive at room temperature[n 33] but is slowly attacked by hot concentrated sulfuric or nitric acid.[312] Germanium also reacts with molten caustic soda to yield sodium germanate Na₂GeO₃ and hydrogen gas.[313] It melts at 938 °C. Germanium is a semiconductor with an electrical conductivity of around 2 × 10⁻² S•cm⁻¹[312] and a band gap of 0.67 eV.[314] Liquid germanium is a metallic conductor, with an electrical conductivity similar to that of liquid mercury.[315]

Most of the chemistry of germanium is characteristic of a nonmetal.[316] Whether or not germanium forms a cation is unclear, aside from the reported existence of the Ge²⁺ ion in a few esoteric compounds.[n 34] It can form alloys with metals such as aluminium and gold.[329] It shows fewer tendencies to anionic behaviour than ordinary nonmetals.[299] Its solution chemistry is characterised by the formation of oxyanions.[300] Germanium generally forms tetravalent (IV) compounds, and it can also form less stable divalent (II) compounds, in which it behaves more like a metal.[330] Germanium analogues of all of the major types of silicates have been prepared.[331] The metallic character of germanium is also suggested by the formation of various oxoacid salts. A phosphate [(HPO₄)₂Ge·H₂O] and highly stable trifluoroacetate Ge(OCOCF₃)₄ have been described, as have Ge₂(SO₄)₂, Ge(ClO₄)₄ and GeH₂(C₂O₄)₃.[332] The oxide GeO₂ is polymeric,[274] amphoteric,[333] and a glass former.[281] The dioxide is soluble in acidic solutions (the monoxide GeO, is even more so), and this is sometimes used to classify germanium as a metal.[334] Up to the 1930s germanium was considered to be a poorly conducting metal;[335] it has occasionally been classified as a metal by later writers.[336] As with all the elements commonly recognised as metalloids, germanium has an established organometallic chemistry (see Organogermanium chemistry).[337]

Arsenic

Main article: Arsenic

Arsenic, sealed in a container to prevent tarnishing

Arsenic is a grey, metallic looking solid. It has a density of 5.727 g/cm³ and is brittle, and moderately hard (more than aluminium; less than iron).[338] It is stable in dry air but develops a golden bronze patina in moist air, which blackens on further exposure. Arsenic is attacked by nitric acid and concentrated sulfuric acid. It reacts with fused caustic soda to give the arsenate Na₃AsO₃ and hydrogen gas.[339] Arsenic sublimes at 615 °C. The vapour is lemon-yellow and smells like garlic.[340] Arsenic only melts under a pressure of 38.6 atm, at 817 °C.[341] It is a semimetal with an electrical conductivity of around 3.9 × 10⁴ S•cm⁻¹[342] and a band overlap of 0.5 eV.[343][n 35] Liquid arsenic is a semiconductor with a band gap of 0.15 eV.[345]

The chemistry of arsenic is predominately nonmetallic.[346] Whether or not arsenic forms a cation is unclear.[n 36] Its many metal alloys are mostly brittle.[354] It shows fewer tendencies to anionic behaviour than ordinary nonmetals.[299] Its solution chemistry is characterised by the formation of oxyanions.[300] Arsenic generally forms compounds in which it has an oxidation state of +3 or +5.[355] The halides, and the oxides and their derivatives are illustrative examples.[302] In the trivalent state, arsenic shows some incipient metallic properties.[356] The halides are hydrolysed by water but these reactions, particularly those of the chloride, are reversible with the addition of a hydrohalic acid.[357] The oxide is acidic but, as noted below, (weakly) amphoteric. The higher, less stable, pentavalent state has strongly acidic (nonmetallic) properties.[358] Compared to phosphorus, the stronger metallic character of arsenic is indicated by the formation of oxoacid salts such as AsPO₄, As₂(SO₄)₃[n 37] and arsenic acetate As(CH₃COO)₃.[361] The oxide As₂O₃ is polymeric,[274] amphoteric,[362][n 38] and a glass former.[281] Arsenic has an extensive organometallic chemistry (see Organoarsenic chemistry).[365]

Antimony

Main article: Antimony

Antimony, showing its brilliant lustre

Antimony is a silver-white solid with a blue tint and a brilliant lustre.[339] It has a density of 6.697 g/cm³ and is brittle, and moderately hard (more so than arsenic; less so than iron; about the same as copper).[338] It is stable in air and moisture at room temperature. It is attacked by concentrated nitric acid, yielding the hydrated pentoxide Sb₂O₅. Aqua regia gives the pentachloride SbCl₅ and hot concentrated sulfuric acid results in the sulfate Sb₂(SO₄)₃.[366] It is not affected by molten alkali.[367] Antimony is capable of displacing hydrogen from water, when heated: 2 Sb + 3 H₂O → Sb₂O₃ + 3 H₂.[368] It melts at 631 °C. Antimony is a semimetal with an electrical conductivity of around 3.1 × 10⁴ S•cm⁻¹[369] and a band overlap of 0.16 eV.[343][n 39] Liquid antimony is a metallic conductor with an electrical conductivity of around 5.3 × 10⁴ S•cm⁻¹.[371]

Most of the chemistry of antimony is characteristic of a nonmetal.[372] Antimony has some definite cationic chemistry,[373] SbO⁺ and Sb(OH)₂⁺ being present in acidic aqueous solution;[374][n 40] the compound Sb₈(GaCl₄)₂, which contains the homopolycation, Sb₈²⁺, was prepared in 2004.[376] It can form alloys with one or more metals such as aluminium,[377] iron, nickel, copper, zinc, tin, lead, and bismuth.[378] Antimony has fewer tendencies to anionic behaviour than ordinary nonmetals.[299] Its solution chemistry is characterised by the formation of oxyanions.[300] Like arsenic, antimony generally forms compounds in which it has an oxidation state of +3 or +5.[355] The halides, and the oxides and their derivatives are illustrative examples.[302] The +5 state is less stable than the +3, but relatively easier to attain than with arsenic. This is explained by the poor shielding afforded the arsenic nucleus by its 3d¹⁰ electrons. In comparison, the tendency of antimony (being a heavier atom) to oxidize more easily partially offsets the effect of its 4d¹⁰ shell.[379] Tripositive antimony is amphoteric; pentapositive antimony is (predominately) acidic.[380] Consistent with an increase in metallic character down group 15, antimony forms salts or salt-like compounds including a nitrate Sb(NO₃)₃, phosphate SbPO₄, sulfate Sb₂(SO₄)₃ and perchlorate Sb(ClO₄)₃.[381] The otherwise acidic pentoxide Sb₂O₅ shows some basic (metallic) behaviour in that it can be dissolved in very acidic solutions, with the formation of the oxycation SbO⁺
₂.[382] The oxide Sb₂O₃ is polymeric,[274] amphoteric,[383] and a glass former.[281] Antimony has an extensive organometallic chemistry (see Organoantimony chemistry).[384]

Tellurium

Main article: Tellurium

Tellurium, described by Dmitri Mendeleev as forming a transition between metals and nonmetals[385]

Tellurium is a silvery-white shiny solid.[386] It has a density of 6.24 g/cm³, is brittle, and is the softest of the commonly recognised metalloids, being marginally harder than sulfur.[338] Large pieces of tellurium are stable in air. The finely powdered form is oxidized by air in the presence of moisture. Tellurium reacts with boiling water, or when freshly precipitated even at 50 °C, to give the dioxide and hydrogen: Te + 2 H₂O → TeO₂ + 2 H₂.[387] It reacts (to varying degrees) with nitric, sulfuric, and hydrochloric acids to give compounds such as the sulfoxide TeSO₃ or tellurous acid H₂TeO₃,[388] the basic nitrate (Te₂O₄H)⁺(NO₃)⁻,[389] or the oxide sulfate Te₂O₃(SO₄).[390] It dissolves in boiling alkalis, to give the tellurite and telluride: 3 Te + 6 KOH = K₂TeO₃ + 2 K₂Te + 3 H₂O, a reaction that proceeds or is reversible with increasing or decreasing temperature.[391]

At higher temperatures tellurium is sufficiently plastic to extrude.[392] It melts at 449.51 °C. Crystalline tellurium has a structure consisting of parallel infinite spiral chains. The bonding between adjacent atoms in a chain is covalent, but there is evidence of a weak metallic interaction between the neighbouring atoms of different chains.[393] Tellurium is a semiconductor with an electrical conductivity of around 1.0 S•cm⁻¹[394] and a band gap of 0.32 to 0.38 eV.[395] Liquid tellurium is a semiconductor, with an electrical conductivity, on melting, of around 1.9 × 10³ S•cm⁻¹.[395] Superheated liquid tellurium is a metallic conductor.[396]

Most of the chemistry of tellurium is characteristic of a nonmetal.[397] It shows some cationic behaviour. The dioxide dissolves in acid to yield the trihydroxotellurium(IV) Te(OH)₃⁺ ion;[398][n 41] the red Te₄²⁺ and yellow-orange Te₆²⁺ ions form when tellurium is oxidized in fluorosulfuric acid (HSO₃F), or liquid sulfur dioxide (SO₂), respectively.[401] It can form alloys with aluminium, silver, and tin.[402] Tellurium shows fewer tendencies to anionic behaviour than ordinary nonmetals.[299] Its solution chemistry is characterised by the formation of oxyanions.[300] Tellurium generally forms compounds in which it has an oxidation state of −2, +4 or +6. The +4 state is the most stable.[387] Tellurides of composition X_xTe_y are easily formed with most other elements and represent the most common tellurium minerals. Nonstoichiometry is pervasive, especially with transition metals. Many tellurides can be regarded as metallic alloys.[403] The increase in metallic character evident in tellurium, as compared to the lighter chalcogens, is further reflected in the reported formation of various other oxyacid salts, such as a basic selenate 2TeO₂·SeO₃ and an analogous perchlorate and periodate 2TeO₂·HXO₄.[404] Tellurium forms a polymeric,[274] amphoteric,[383] glass-forming oxide[281] TeO₂. It is a "conditional" glass-forming oxide—it forms a glass with a very small amount of additive.[281] Tellurium has an extensive organometallic chemistry (see Organotellurium chemistry).[405]

Elements less commonly recognised as metalloids

Carbon

Main article: Carbon

Carbon (as graphite). Delocalized valence electrons within the layers of graphite give it a metallic appearance.[406]

Carbon is ordinarily classified as a nonmetal[407] but has some metallic properties and is occasionally classified as a metalloid.[408] Hexagonal graphitic carbon (graphite) is the most thermodynamically stable allotrope of carbon under ambient conditions.[409] It has a lustrous appearance[410] and is a fairly good electrical conductor.[411] Graphite has a layered structure. Each layer consists of carbon atoms bonded to three other carbon atoms in a hexagonal lattice arrangement. The layers are stacked together and held loosely by van der Waals forces and delocalized valence electrons.[412]

Like a metal, the conductivity of graphite in the direction of its planes decreases as the temperature is raised;[413][n 42] it has the electronic band structure of a semimetal.[413] The allotropes of carbon, including graphite, can accept foreign atoms or compounds into their structures via substitution, intercalation, or doping. The resulting materials are referred to as "carbon alloys".[417] Carbon can form ionic salts, including a hydrogen sulfate, perchlorate, and nitrate (C⁺
₂₄X⁻.2HX, where X = HSO₄, ClO₄; and C⁺
₂₄NO^–
₃.3HNO₃).[418][n 43] In organic chemistry, carbon can form complex cations—termed carbocations—in which the positive charge is on the carbon atom; examples are CH⁺
₃ and CH⁺
₅, and their derivatives.[419]

Carbon is brittle,[420] and behaves as a semiconductor in a direction perpendicular to its planes.[413] Most of its chemistry is nonmetallic;[421] it has a relatively high ionization energy[422] and, compared to most metals, a relatively high electronegativity.[423] Carbon can form anions such as C⁴⁻ (methanide), C^2–
₂ (acetylide), and C^3–
₄ (sesquicarbide or allylenide), in compounds with metals of main groups 1–3, and with the lanthanides and actinides.[424] Its oxide CO₂ forms carbonic acid H₂CO₃.[425][n 44]

Aluminium

Main article: Aluminium

High purity aluminium is much softer than its familiar alloys. People who handle it for the first time often ask if it is the real thing.[427]

Aluminium is ordinarily classified as a metal.[428] It is lustrous, malleable and ductile, and has high electrical and thermal conductivity. Like most metals it has a close-packed crystalline structure,[429] and forms a cation in aqueous solution.[430]

It has some properties that are unusual for a metal; taken together,[431] these are sometimes used as a basis to classify aluminium as a metalloid.[432] Its crystalline structure shows some evidence of directional bonding.[433] Aluminium bonds covalently in most compounds.[434] The oxide Al₂O₃ is amphoteric[435] and a conditional glass-former.[281] Aluminium can form anionic aluminates,[431] such behaviour being considered nonmetallic in character.[69]

Classifying aluminium as a metalloid has been disputed[436] given its many metallic properties. It is therefore, arguably, an exception to the mnemonic that elements adjacent to the metal–nonmetal dividing line are metalloids.[437][n 45]

Stott[439] labels aluminium as a weak metal. It has the physical properties of a metal but some of the chemical properties of a nonmetal. Steele[440] notes the paradoxical chemical behaviour of aluminium: "It resembles a weak metal in its amphoteric oxide and in the covalent character of many of its compounds ... Yet it is a highly electropositive metal ... [with] a high negative electrode potential". Moody[441] says that, "aluminium is on the 'diagonal borderland' between metals and non-metals in the chemical sense."

Selenium

Main article: Selenium

Grey selenium, being a photoconductor, conducts electricity around 1,000 times better when light falls on it, a property used since the mid-1870s in various light-sensing applications[442]

Selenium shows borderline metalloid or nonmetal behaviour.[443][n 46]

Its most stable form, the grey trigonal allotrope, is sometimes called "metallic" selenium because its electrical conductivity is several orders of magnitude greater than that of the red monoclinic form.[446] The metallic character of selenium is further shown by its lustre,[447] and its crystalline structure, which is thought to include weakly "metallic" interchain bonding.[448] Selenium can be drawn into thin threads when molten and viscous.[449] It shows reluctance to acquire "the high positive oxidation numbers characteristic of nonmetals".[450] It can form cyclic polycations (such as Se²⁺
₈) when dissolved in oleums[451] (an attribute it shares with sulfur and tellurium), and a hydrolysed cationic salt in the form of trihydroxoselenium(IV) perchlorate [Se(OH)₃]⁺·ClO^–
₄.[452]

The nonmetallic character of selenium is shown by its brittleness[447] and the low electrical conductivity (~10⁻⁹ to 10⁻¹² S•cm⁻¹) of its highly purified form.[93] This is comparable to or less than that of bromine (7.95×10^–12 S•cm⁻¹),[453] a nonmetal. Selenium has the electronic band structure of a semiconductor[454] and retains its semiconducting properties in liquid form.[454] It has a relatively high[455] electronegativity (2.55 revised Pauling scale). Its reaction chemistry is mainly that of its nonmetallic anionic forms Se²⁻, SeO²⁻
₃ and SeO²⁻
₄.[456]

Selenium is commonly described as a metalloid in the environmental chemistry literature.[457] It moves through the aquatic environment similarly to arsenic and antimony;[458] its water-soluble salts, in higher concentrations, have a similar toxicological profile to that of arsenic.[459]

Polonium

Main article: Polonium

Polonium is "distinctly metallic" in some ways.[240] Both of its allotropic forms are metallic conductors.[240] It is soluble in acids, forming the rose-coloured Po²⁺ cation and displacing hydrogen: Po + 2 H⁺ → Po²⁺ + H₂.[460] Many polonium salts are known.[461] The oxide PoO₂ is predominantly basic in nature.[462] Polonium is a reluctant oxidizing agent, unlike its lightest congener oxygen: highly reducing conditions are required for the formation of the Po²⁻ anion in aqueous solution.[463]

Whether polonium is ductile or brittle is unclear. It is predicted to be ductile based on its calculated elastic constants.[464] It has a simple cubic crystalline structure. Such a structure has few slip systems and "leads to very low ductility and hence low fracture resistance".[465]

Polonium shows nonmetallic character in its halides, and by the existence of polonides. The halides have properties generally characteristic of nonmetal halides (being volatile, easily hydrolyzed, and soluble in organic solvents).[466] Many metal polonides, obtained by heating the elements together at 500–1,000 °C, and containing the Po²⁻ anion, are also known.[467]

Astatine

Main article: Astatine

As a halogen, astatine tends to be classified as a nonmetal.[468] It has some marked metallic properties[469] and is sometimes instead classified as either a metalloid[470] or (less often) as a metal.[n 47] Immediately following its production in 1940, early investigators considered it a metal.[472] In 1949 it was called the most noble (difficult to reduce) nonmetal as well as being a relatively noble (difficult to oxidize) metal.[473] In 1950 astatine was described as a halogen and (therefore) a reactive nonmetal.[474] In 2013, on the basis of relativistic modelling, astatine was predicted to be a monatomic metal, with a face-centred cubic crystalline structure.[475]

Several authors have commented on the metallic nature of some of the properties of astatine. Since iodine is a semiconductor in the direction of its planes, and since the halogens become more metallic with increasing atomic number, it has been presumed that astatine would be a metal if it could form a condensed phase.[476][n 48] Astatine may be metallic in the liquid state on the basis that elements with an enthalpy of vaporization (∆H_vap) greater than ~42 kJ/mol are metallic when liquid.[478] Such elements include boron,[n 49] silicon, germanium, antimony, selenium, and tellurium. Estimated values for ∆H_vap of diatomic astatine are 50 kJ/mol or higher;[482] diatomic iodine, with a ∆H_vap of 41.71,[483] falls just short of the threshold figure.

"Like typical metals, it [astatine] is precipitated by hydrogen sulfide even from strongly acid solutions and is displaced in a free form from sulfate solutions; it is deposited on the cathode on electrolysis."[484][n 50] Further indications of a tendency for astatine to behave like a (heavy) metal are: "... the formation of pseudohalide compounds ... complexes of astatine cations ... complex anions of trivalent astatine ... as well as complexes with a variety of organic solvents".[486] It has also been argued that astatine demonstrates cationic behaviour, by way of stable At⁺ and AtO⁺ forms, in strongly acidic aqueous solutions.[487]

Some of astatine's reported properties are nonmetallic. It has been extrapolated to have the narrow liquid range ordinarily associated with nonmetals (mp 302 °C; bp 337 °C),[488] although experimental indications suggest a lower boiling point of about 230±3 °C. Batsanov gives a calculated band gap energy for astatine of 0.7 eV;[489] this is consistent with nonmetals (in physics) having separated valence and conduction bands and thereby being either semiconductors or insulators.[490] The chemistry of astatine in aqueous solution is mainly characterised by the formation of various anionic species.[491] Most of its known compounds resemble those of iodine,[492] which is a halogen and a nonmetal.[493] Such compounds include astatides (XAt), astatates (XAtO₃), and monovalent interhalogen compounds.[494]

Restrepo et al.[495] reported that astatine appeared to be more polonium-like than halogen-like. They did so on the basis of detailed comparative studies of the known and interpolated properties of 72 elements.

Related concepts

Near metalloids

Iodine crystals, showing a metallic lustre. Iodine is a semiconductor in the direction of its planes, with a band gap of ~1.3 eV. It has an electrical conductivity of 1.7 × 10⁻⁸ S•cm⁻¹ at room temperature.[496] This is higher than selenium but lower than boron, the least electrically conducting of the recognised metalloids.[n 51]

In the periodic table, some of the elements adjacent to the commonly recognised metalloids, although usually classified as either metals or nonmetals, are occasionally referred to as near-metalloids[499] or noted for their metalloidal character. To the left of the metal–nonmetal dividing line, such elements include gallium,[500] tin[501] and bismuth.[502] They show unusual packing structures,[503] marked covalent chemistry (molecular or polymeric),[504] and amphoterism.[505] To the right of the dividing line are carbon,[506] phosphorus,[507] selenium[508] and iodine.[509] They exhibit metallic lustre, semiconducting properties[n 52] and bonding or valence bands with delocalized character. This applies to their most thermodynamically stable forms under ambient conditions: carbon as graphite; phosphorus as black phosphorus;[n 53] and selenium as grey selenium.

Allotropes

White tin (left) and grey tin (right). Both forms have a metallic appearance.

Different crystalline forms of an element are called allotropes. Some allotropes, particularly those of elements located (in periodic table terms) alongside or near the notional dividing line between metals and nonmetals, exhibit more pronounced metallic, metalloidal or nonmetallic behaviour than others.[515] The existence of such allotropes can complicate the classification of the elements involved.[516]

Tin, for example, has two allotropes: tetragonal "white" β-tin and cubic "grey" α-tin. White tin is a very shiny, ductile and malleable metal. It is the stable form at or above room temperature and has an electrical conductivity of 9.17 × 10⁴ S·cm⁻¹ (~1/6th that of copper).[517] Grey tin usually has the appearance of a grey micro-crystalline powder, and can also be prepared in brittle semi-lustrous crystalline or polycrystalline forms. It is the stable form below 13.2 °C and has an electrical conductivity of between (2–5) × 10² S·cm⁻¹ (~1/250th that of white tin).[518] Grey tin has the same crystalline structure as that of diamond. It behaves as a semiconductor (as if it had a band gap of 0.08 eV), but has the electronic band structure of a semimetal.[519] It has been referred to as either a very poor metal,[520] a metalloid,[521] a nonmetal[522] or a near metalloid.[502]

The diamond allotrope of carbon is clearly nonmetallic, being translucent and having a low electrical conductivity of 10⁻¹⁴ to 10⁻¹⁶ S·cm⁻¹.[523] Graphite has an electrical conductivity of 3 × 10⁴ S·cm⁻¹,[524] a figure more characteristic of a metal. Phosphorus, sulfur, arsenic, selenium, antimony, and bismuth also have less stable allotropes that display different behaviours.[525]

Abundance, extraction, and cost

Abundance

Z	Element	Grams /tonne
8	Oxygen	461,000
14	Silicon	282,000
13	Aluminium	82,300
26	Iron	56,300
6	Carbon	200
29	Copper	60
5	Boron	10
33	Arsenic	1.8
32	Germanium	1.5
47	Silver	0.075
34	Selenium	0.05
51	Antimony	0.02
79	Gold	0.004
52	Tellurium	0.001
75	Rhenium	0.00000000077×10^−10
54	Xenon	0.000000000033×10^−11
84	Polonium	0.00000000000000022×10^−16
85	Astatine	0.0000000000000000033×10^−20

The table gives crustal abundances of the elements commonly to rarely recognised as metalloids.[526] Some other elements are included for comparison: oxygen and xenon (the most and least abundant elements with stable isotopes); iron and the coinage metals copper, silver, and gold; and rhenium, the least abundant stable metal (aluminium is normally the most abundant metal). Various abundance estimates have been published; these often disagree to some extent.[527]

Extraction

The recognised metalloids can be obtained by chemical reduction of either their oxides or their sulfides. Simpler or more complex extraction methods may be employed depending on the starting form and economic factors.[528] Boron is routinely obtained by reducing the trioxide with magnesium: B₂O₃ + 3 Mg → 2 B + 3MgO; after secondary processing the resulting brown powder has a purity of up to 97%.[529] Boron of higher purity (> 99%) is prepared by heating volatile boron compounds, such as BCl₃ or BBr₃, either in a hydrogen atmosphere (2 BX₃ + 3 H₂ → 2 B + 6 HX) or to the point of thermal decomposition. Silicon and germanium are obtained from their oxides by heating the oxide with carbon or hydrogen: SiO₂ + C → Si + CO₂; GeO₂ + 2 H₂ → Ge + 2 H₂O. Arsenic is isolated from its pyrite (FeAsS) or arsenical pyrite (FeAs₂) by heating; alternatively, it can be obtained from its oxide by reduction with carbon: 2 As₂O₃ + 3 C → 2 As + 3 CO₂.[530] Antimony is derived from its sulfide by reduction with iron: Sb₂S₃ → 2 Sb + 3 FeS. Tellurium is prepared from its oxide by dissolving it in aqueous NaOH, yielding tellurite, then by electrolytic reduction: TeO₂ + 2 NaOH → Na₂TeO₃ + H₂O;[531] Na₂TeO₃ + H₂O → Te + 2 NaOH + O₂.[532] Another option is reduction of the oxide by roasting with carbon: TeO₂ + C → Te + CO₂.[533]

Production methods for the elements less frequently recognised as metalloids involve natural processing, electrolytic or chemical reduction, or irradiation. Carbon (as graphite) occurs naturally and is extracted by crushing the parent rock and floating the lighter graphite to the surface. Aluminium is extracted by dissolving its oxide Al₂O₃ in molten cryolite Na₃AlF₆ and then by high temperature electrolytic reduction. Selenium is produced by roasting the coinage metal selenides X₂Se (X = Cu, Ag, Au) with soda ash to give the selenite: X₂Se + O₂ + Na₂CO₃ → Na₂SeO₃ + 2 X + CO₂; the selenide is neutralized by sulfuric acid H₂SO₄ to give selenous acid H₂SeO₃; this is reduced by bubbling with SO₂ to yield elemental selenium. Polonium and astatine are produced in minute quantities by irradiating bismuth.[534]

Cost

The recognised metalloids and their closer neighbours mostly cost less than silver; only polonium and astatine are more expensive than gold, on account of their significant radioactivity. As of 5 April 2014, prices for small samples (up to 100 g) of silicon, antimony and tellurium, and graphite, aluminium and selenium, average around one third the cost of silver (US$1.5 per gram or about $45 an ounce). Boron, germanium, and arsenic samples average about three-and-a-half times the cost of silver.[n 54] Polonium is available for about $100 per microgram.[535] Zalutsky and Pruszynski[536] estimate a similar cost for producing astatine. Prices for the applicable elements traded as commodities tend to range from two to three times cheaper than the sample price (Ge), to nearly three thousand times cheaper (As).[n 55]

See also

• Properties of metals, metalloids, and nonmetals
• Lists of metalloids

Notes

1. For a related commentary see also: Vernon RE 2013, 'Which Elements Are Metalloids?', Journal of Chemical Education, vol. 90, no. 12, pp. 1703–1707, doi:10.1021/ed3008457
2. Definitions and extracts by different authors, illustrating aspects of the generic definition, follow:
   • "In chemistry a metalloid is an element with properties intermediate between those of metals and nonmetals."[3]
   • "Between the metals and nonmetals in the periodic table we find elements ... [that] share some of the characteristic properties of both the metals and nonmetals, making it difficult to place them in either of these two main categories"[4]
   • "Chemists sometimes use the name metalloid ... for these elements which are difficult to classify one way or the other."[5]
   • "Because the traits distinguishing metals and nonmetals are qualitative in nature, some elements do not fall unambiguously in either category. These elements ... are called metalloids ..."[6]
   More broadly, metalloids have been referred to as:
   • "elements that ... are somewhat of a cross between metals and nonmetals";[7] or
   • "weird in-between elements".[8]
3. Gold, for example, has mixed properties but is still recognised as "king of metals". Besides metallic behaviour (such as high electrical conductivity, and cation formation), gold shows nonmetallic behaviour:
   • It has the highest electrode potential
   • It has the third-highest ionization energy among the metals (after zinc and mercury)
   • It has the lowest electron affinity
   • Its electronegativity of 2.54 is highest among the metals and exceeds that of some nonmetals (hydrogen 2.2; phosphorus 2.19; and radon 2.2)
   • It forms the Au⁻ auride anion, acting in this way like a halogen
   • It sometimes has a tendency, known as "aurophilicity", to bond to itself.[11]
   On halogen character, see also Belpassi et al.,[12] who conclude that in the aurides MAu (M = Li–Cs) gold "behaves as a halogen, intermediate between Br and I"; on aurophilicity, see also Schmidbaur and Schier.[13]
4. Mann et al.[16] refer to these elements as "the recognized metalloids".
5. Jones[44] writes: "Though classification is an essential feature in all branches of science, there are always hard cases at the boundaries. Indeed, the boundary of a class is rarely sharp."
6. The lack of a standard division of the elements into metals, metalloids, and nonmetals is not necessarily an issue. There is more or less, a continuous progression from the metallic to the nonmetallic. A specified subset of this continuum could serve its particular purpose as well as any other.[45]
7. The packing efficiency of boron is 38%; silicon and germanium 34; arsenic 38.5; antimony 41; and tellurium 36.4.[49] These values are lower than in most metals (80% of which have a packing efficiency of at least 68%),[50] but higher than those of elements usually classified as nonmetals. (Gallium is unusual, for a metal, in having a packing efficiency of just 39%.)[51] Other notable values for metals are 42.9 for bismuth[52] and 58.5 for liquid mercury.[53]) Packing efficiencies for nonmetals are: graphite 17%,[54] sulfur 19.2,[55] iodine 23.9,[55] selenium 24.2,[55] and black phosphorus 28.5.[52]
8. More specifically, the Goldhammer-Herzfeld criterion is the ratio of the force holding an individual atom's valence electrons in place with the forces on the same electrons from interactions between the atoms in the solid or liquid element. When the interatomic forces are greater than, or equal to, the atomic force, valence electron itinerancy is indicated and metallic behaviour is predicted.[57] Otherwise nonmetallic behaviour is anticipated.
9. As the ratio is based on classical arguments[59] it does not accommodate the finding that polonium, which has a value of ~0.95, adopts a metallic (rather than covalent) crystalline structure, on relativistic grounds.[60] Even so it offers a first order rationalization for the occurrence of metallic character amongst the elements.[61]
10. Atomic conductance is the electrical conductivity of one mole of a substance. It is equal to electrical conductivity divided by molar volume.[5]
11. Selenium has an ionization energy (IE) of 225 kcal/mol (941 kJ/mol) and is sometimes described as a semiconductor. It has a relatively high 2.55 electronegativity (EN). Polonium has an IE of 194 kcal/mol (812 kJ/mol) and a 2.0 EN, but has a metallic band structure.[66] Astatine has an IE of 215 kJ/mol (899 kJ/mol) and an EN of 2.2.[67] Its electronic band structure is not known with any certainty.
12. Oderberg[80] argues on ontological grounds that anything not a metal is therefore a nonmetal, and that this includes semi-metals (i.e. metalloids).
13. Copernicium is reportedly the only metal thought to be a gas at room temperature.[86]
14. Metals have electrical conductivity values of from 6.9 × 10³ S•cm⁻¹ for manganese to 6.3 × 10⁵ for silver.[90]
15. Metalloids have electrical conductivity values of from 1.5 × 10⁻⁶ S•cm⁻¹ for boron to 3.9 × 10⁴ for arsenic.[92] If selenium is included as a metalloid the applicable conductivity range would start from ~10⁻⁹ to 10⁻¹² S•cm⁻¹.[93]
16. Nonmetals have electrical conductivity values of from ~10⁻¹⁸ S•cm⁻¹ for the elemental gases to 3 × 10⁴ in graphite.[94]
17. Chedd[101] defines metalloids as having electronegativity values of 1.8 to 2.2 (Allred-Rochow scale). He included boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine in this category. In reviewing Chedd's work, Adler[102] described this choice as arbitrary, as other elements whose electronegativities lie in this range include copper, silver, phosphorus, mercury, and bismuth. He went on to suggest defining a metalloid as "a semiconductor or semimetal" and to include bismuth and selenium in this category.
18. Olmsted and Williams[106] commented that, "Until quite recently, chemical interest in the metalloids consisted mainly of isolated curiosities, such as the poisonous nature of arsenic and the mildly therapeutic value of borax. With the development of metalloid semiconductors, however, these elements have become among the most intensely studied".
19. Research published in 2012 suggests that metal-metalloid glasses can be characterised by an interconnected atomic packing scheme in which metallic and covalent bonding structures coexist.[174]
20. The reaction involved is Ge + 2 MoO₃ → GeO₂ + 2 MoO₂. Adding arsenic or antimony (n-type electron donors) increases the rate of reaction; adding gallium or indium (p-type electron acceptors) decreases it.[188]
21. Ellern, writing in Military and Civilian Pyrotechnics (1968), comments that carbon black "has been specified for and used in a nuclear air-burst simulator."[194]
22. For a post-1960 example of the former use of the term metalloid to refer to nonmetals see Zhdanov,[243] who divides the elements into metals; intermediate elements (H, B, C, Si, Ge, Se, Te); and metalloids (of which the most typical are given as O, F, and Cl).
23. Boron, at 1.56 eV, has the largest band gap amongst the commonly recognised (semiconducting) metalloids. Of nearby elements in periodic table terms, selenium has the next highest band gap (close to 1.8 eV) followed by white phosphorus (around 2.1 eV).[254]
24. The synthesis of B₄₀ borospherene, a "distorted fullerene with a hexagonal hole on the top and bottom and four heptagonal holes around the waist" was announced in 2014.[258]
25. The BH₃ and Fe(CO₄) species in these reactions are short-lived reaction intermediates.[266]
26. On the analogy between boron and metals, Greenwood[268] commented that: "The extent to which metallic elements mimic boron (in having fewer electrons than orbitals available for bonding) has been a fruitful cohering concept in the development of metalloborane chemistry ... Indeed, metals have been referred to as "honorary boron atoms" or even as "flexiboron atoms". The converse of this relationship is clearly also valid ..."
27. The bonding in boron trifluoride, a gas, has been referred to as predominately ionic[272] a description which was subsequently described as misleading.[273]
28. Boron trioxide B₂O₃ is sometimes described as being (weakly) amphoteric.[276] It reacts with alkalies to give various borates.[277] In its hydrated form (as H₃BO₃, boric acid) it reacts with sulfur trioxide, the anhydride of sulfuric acid, to form a bisulfate B(HSO₃) ₄.[278] In its pure (anhydrous) form it reacts with phosphoric acid to form a "phosphate" BPO₄.[279] The latter compound may be regarded as a mixed oxide of B₂O₃ and P₂O₅.[280]
29. Organic derivatives of metalloids are traditionally counted as organometallic compounds.[282]
30. In air, silicon forms a thin coating of amorphous silicon dioxide, 2 to 3 nm thick.[287] This coating is dissolved by hydrogen fluoride at a very low pace—on the order of two to three hours per nanometre.[288] Silicon dioxide, and silicate glasses (of which silicon dioxide is a major component), are otherwise readily attacked by hydrofluoric acid.[289]
31. The bonding in silicon tetrafluoride, a gas, has been referred to as predominately ionic[272] a description which was subsequently described as misleading.[273]
32. Although SiO₂ is classified as an acidic oxide, and hence reacts with alkalis to give silicates, it reacts with phosphoric acid to yield a silicon oxide orthophosphate Si₅O(PO₄)₆,[305] and with hydrofluoric acid to give hexafluorosilicic acid H₂SiF₆.[306] The latter reaction "is sometimes quoted as evidence of basic [that is, metallic] properties".[307]
33. Temperatures above 400 °C are required to form a noticeable surface oxide layer.[311]
34. Sources mentioning germanium cations include: Powell & Brewer[317] who state that the cadmium iodide CdI₂ structure of germanous iodide GeI₂ establishes the existence of the Ge⁺⁺ ion (the CdI₂ structure being found, according to Ladd,[318] in "many metallic halides, hydroxides, and chalcides"); Everest[319] who comments that, "it seems probable that the Ge⁺⁺ ion can also occur in other crystalline germanous salts such as the phosphite, which is similar to the salt-like stannous phosphite and germanous phosphate, which resembles not only the stannous phosphates, but the manganous phosphates also"; Pan, Fu & Huang[320] who presume the formation of the simple Ge⁺⁺ ion when Ge(OH)₂ is dissolved in a perchloric acid solution, on the basis that, "ClO4⁻ has little tendency to enter complex formation with a cation"; Monconduit et al.[321] who prepared the layer compound or phase Nb₃Ge_xTe₆ (x ≃ 0.9), and reported that this contained a Ge^II cation; Richens[322] who records that, "Ge²⁺ (aq) or possibly Ge(OH)⁺(aq) is said to exist in dilute air-free aqueous suspensions of the yellow hydrous monoxide…however both are unstable with respect to the ready formation of GeO₂.nH₂O"; Rupar et al.[323] who synthesized a cryptand compound containing a Ge²⁺ cation; and Schwietzer and Pesterfield[324] who write that, "the monoxide GeO dissolves in dilute acids to give Ge⁺² and in dilute bases to produce GeO₂⁻², all three entities being unstable in water". Sources dismissing germanium cations or further qualifying their presumed existence include: Jolly and Latimer[325] who assert that, "the germanous ion cannot be studied directly because no germanium (II) species exists in any appreciable concentration in noncomplexing aqueous solutions"; Lidin[326] who says that, "[germanium] forms no aquacations"; Ladd[327] who notes that the CdI₂ structure is "intermediate in type between ionic and molecular compounds"; and Wiberg[328] who states that, "no germanium cations are known".
35. Arsenic also exists as a naturally occurring (but rare) allotrope (arsenolamprite), a crystalline semiconductor with a band gap of around 0.3 eV or 0.4 eV. It can also be prepared in a semiconducting amorphous form, with a band gap of around 1.2–1.4 eV.[344]
36. Sources mentioning cationic arsenic include: Gillespie & Robinson[347] who find that, "in very dilute solutions in 100% sulphuric acid, arsenic (III) oxide forms arsonyl (III) hydrogen sulphate, AsO.HO₄, which is partly ionized to give the AsO⁺ cation. Both these species probably exist mainly in solvated forms, e.g., As(OH)(SO₄H)₂, and As(OH)(SO₄H)⁺ respectively"; Paul et al.[348] who reported spectroscopic evidence for the presence of As₄²⁺ and As₂²⁺ cations when arsenic was oxidized with peroxydisulfuryl difluoride S₂O₆F₂ in highly acidic media (Gillespie and Passmore[349] noted the spectra of these species were very similar to S₄²⁺ and S₈²⁺ and concluded that, "at present" there was no reliable evidence for any homopolycations of arsenic); Van Muylder and Pourbaix,[350] who write that, "As₂O₃ is an amphoteric oxide which dissolves in water and in solutions of pH between 1 and 8 with the formation of undissociated arsenious acid HAsO₂; the solubility…increases at pH’s below 1 with the formation of 'arsenyl' ions AsO⁺…"; Kolthoff and Elving[351] who write that, "the As³⁺ cation exists to some extent only in strongly acid solutions; under less acid conditions the tendency is toward hydrolysis, so that the anionic form predominates"; Moody[352] who observes that, "arsenic trioxide, As₄O₆, and arsenious acid, H₃AsO₃, are apparently amphoteric but no cations, As³⁺, As(OH)²⁺ or As(OH)₂⁺ are known"; and Cotton et al.[353] who write that (in aqueous solution) the simple arsenic cation As³⁺ "may occur to some slight extent [along with the AsO⁺ cation]" and that, "Raman spectra show that in acid solutions of As₄O₆ the only detectable species is the pyramidal As(OH)₃".
37. The formulae of AsPO₄ and As₂(SO₄)₃ suggest straightforward ionic formulations, with As³⁺, but this is not the case. AsPO₄, "which is virtually a covalent oxide", has been referred to as a double oxide, of the form As₂O₃·P₂O₅. It consists of AsO₃ pyramids and PO₄ tetrahedra, joined together by all their corner atoms to form a continuous polymeric network.[359] As₂(SO₄)₃ has a structure in which each SO₄ tetrahedron is bridged by two AsO₃ trigonal pyramida.[360]
38. As₂O₃ is usually regarded as being amphoteric but a few sources say it is (weakly)[363] acidic. They describe its "basic" properties (its reaction with concentrated hydrochloric acid to form arsenic trichloride) as being alcoholic, in analogy with the formation of covalent alkyl chlorides by covalent alcohols (e.g., R-OH + HCl → RCl + H₂O)[364]
39. Antimony can also be prepared in an amorphous semiconducting black form, with an estimated (temperature-dependent) band gap of 0.06–0.18 eV.[370]
40. Lidin[375] asserts that SbO⁺ does not exist and that the stable form of Sb(III) in aqueous solution is an incomplete hydrocomplex [Sb(H₂O)₄(OH)₂]⁺.
41. Cotton et al.[399] note that TeO₂ appears to have an ionic lattice; Wells[400] suggests that the Te–O bonds have "considerable covalent character".
42. Liquid carbon may[414] or may not[415] be a metallic conductor, depending on pressure and temperature; see also.[416]
43. For the sulfate, the method of preparation is (careful) direct oxidation of graphite in concentrated sulfuric acid by an oxidising agent, such as nitric acid, chromium trioxide or ammonium persulfate; in this instance the concentrated sulfuric acid is acting as an inorganic nonaqueous solvent.
44. Only a small fraction of dissolved CO₂ is present in water as carbonic acid so, even though H₂CO₃ is a medium-strong acid, solutions of carbonic acid are only weakly acidic.[426]
45. A mnemonic that captures the elements commonly recognised as metalloids goes: Up, up-down, up-down, up ... are the metalloids![438]
46. Rochow,[444] who later wrote his 1966 monograph The metalloids,[445] commented that, "In some respects selenium acts like a metalloid and tellurium certainly does".
47. A further option is to include astatine both as a nonmetal and as a metalloid.[471]
48. A visible piece of astatine would be immediately and completely vaporized because of the heat generated by its intense radioactivity.[477]
49. The literature is contradictory as to whether boron exhibits metallic conductivity in liquid form. Krishnan et al.[479] found that liquid boron behaved like a metal. Glorieux et al.[480] characterised liquid boron as a semiconductor, on the basis of its low electrical conductivity. Millot et al.[481] reported that the emissivity of liquid boron was not consistent with that of a liquid metal.
50. Korenman[485] similarly noted that "the ability to precipitate with hydrogen sulfide distinguishes astatine from other halogens and brings it closer to bismuth and other heavy metals".
51. The separation between molecules in the layers of iodine (350 pm) is much less than the separation between iodine layers (427 pm; cf. twice the van der Waals radius of 430 pm).[497] This is thought to be caused by electronic interactions between the molecules in each layer of iodine, which in turn give rise to its semiconducting properties and shiny appearance.[498]
52. For example: intermediate electrical conductivity;[510] a relatively narrow band gap;[511] light sensitivity.[510]
53. White phosphorus is the least stable and most reactive form.[512] It is also the most common, industrially important,[513] and easily reproducible allotrope, and for these three reasons is regarded as the standard state of the element.[514]
54. Sample prices of gold, in comparison, start at roughly thirty-five times that of silver. Based on sample prices for B, C, Al, Si, Ge, As, Se, Ag, Sb, Te, and Au available on-line from Alfa Aesa; Goodfellow; Metallium; and United Nuclear Scientific.
55. Based on spot prices for Al, Si, Ge, As, Sb, Se, and Te available on-line from FastMarkets: Minor Metals; Fast Markets: Base Metals; EnergyTrend: PV Market Status, Polysilicon; and Metal-Pages: Arsenic metal prices, news, and information.

References

1. Chedd 1969, pp. 58, 78; National Research Council 1984, p.  43
2. Atkins et al. 2010, p. 20
3. Cusack 1987, p. 360
4. Kelter, Mosher & Scott 2009, p. 268
5. Hill & Holman 2000, p. 41
6. King 1979, p. 13
7. Moore 2011, p. 81
8. Gray 2010
9. Hopkins & Bailar 1956, p. 458
10. Glinka 1965, p. 77
11. Wiberg 2001, p. 1279
12. Belpassi et al. 2006, pp. 4543–4
13. Schmidbaur & Schier 2008, pp. 1931–51
14. Tyler Miller 1987, p. 59
15. Goldsmith 1982, p. 526; Kotz, Treichel & Weaver 2009, p. 62; Bettelheim et al. 2010, p. 46
16. Mann et al. 2000, p. 2783
17. Hawkes 2001, p. 1686; Segal 1989, p. 965; McMurray & Fay 2009, p. 767
18. Bucat 1983, p. 26; Brown c. 2007
19. Swift & Schaefer 1962, p. 100
20. Hawkes 2001, p. 1686; Hawkes 2010; Holt, Rinehart & Wilson c. 2007
21. Dunstan 1968, pp. 310, 409. Dunstan lists Be, Al, Ge (maybe), As, Se (maybe), Sn, Sb, Te, Pb, Bi, and Po as metalloids (pp. 310, 323, 409, 419).
22. Tilden 1876, pp. 172, 198–201; Smith 1994, p. 252; Bodner & Pardue 1993, p. 354
23. Bassett et al. 1966, p. 127
24. Rausch 1960
25. Thayer 1977, p. 604; Warren & Geballe 1981; Masters & Ela 2008, p. 190
26. Warren & Geballe 1981; Chalmers 1959, p. 72; US Bureau of Naval Personnel 1965, p. 26
27. Siebring 1967, p. 513
28. Wiberg 2001, p. 282
29. Rausch 1960; Friend 1953, p. 68
30. Murray 1928, p. 1295
31. Hampel & Hawley 1966, p. 950; Stein 1985; Stein 1987, pp. 240, 247–8
32. Hatcher 1949, p. 223; Secrist & Powers 1966, p. 459
33. Taylor 1960, p. 614
34. Considine & Considine 1984, p. 568; Cegielski 1998, p. 147; The American heritage science dictionary 2005 p. 397
35. Woodward 1948, p. 1
36. NIST 2010. Values shown in the above table have been converted from the NIST values, which are given in eV.
37. Berger 1997; Lovett 1977, p. 3
38. Goldsmith 1982, p. 526; Hawkes 2001, p. 1686
39. Hawkes 2001, p. 1687
40. Sharp 1981, p. 299
41. Emsley 1971, p. 1
42. James et al. 2000, p. 480
43. Chatt 1951, p. 417 "The boundary between metals and metalloids is indefinite ..."; Burrows et al. 2009, p. 1192: "Although the elements are conveniently described as metals, metalloids, and nonmetals, the transitions are not exact ..."
44. Jones 2010, p. 170
45. Kneen, Rogers & Simpson 1972, pp. 218–220
46. Rochow 1966, pp. 1, 4–7
47. Rochow 1977, p. 76; Mann et al. 2000, p. 2783
48. Askeland, Phulé & Wright 2011, p. 69
49. Van Setten et al. 2007, pp. 2460–1; Russell & Lee 2005, p. 7 (Si, Ge); Pearson 1972, p. 264 (As, Sb, Te; also black P)
50. Russell & Lee 2005, p. 1
51. Russell & Lee 2005, pp. 6–7, 387
52. Pearson 1972, p. 264
53. Okajima & Shomoji 1972, p. 258
54. Kitaĭgorodskiĭ 1961, p. 108
55. Neuburger 1936
56. Edwards & Sienko 1983, p. 693
57. Herzfeld 1927; Edwards 2000, pp. 100–3
58. Edwards & Sienko 1983, p. 695; Edwards et al. 2010
59. Edwards 1999, p. 416
60. Steurer 2007, p. 142; Pyykkö 2012, p. 56
61. Edwards & Sienko 1983, p. 695
62. Hill & Holman 2000, p. 41. They characterise metalloids (in part) on the basis that they are "poor conductors of electricity with atomic conductance usually less than 10⁻³ but greater than 10⁻⁵ ohm⁻¹ cm⁻⁴".
63. Bond 2005, p. 3: "One criterion for distinguishing semi-metals from true metals under normal conditions is that the bulk coordination number of the former is never greater than eight, while for metals it is usually twelve (or more, if for the body-centred cubic structure one counts next-nearest neighbours as well)."
64. Jones 2010, p. 169
65. Masterton & Slowinski 1977, p. 160 list B, Si, Ge, As, Sb, and Te as metalloids, and comment that Po and At are ordinarily classified as metalloids but add that this is arbitrary as so little is known about them.
66. Kraig, Roundy & Cohen 2004, p. 412; Alloul 2010, p. 83
67. Vernon 2013, pp. 1704
68. Vernon 2013, pp. 1703
69. Hamm 1969, p. 653
70. Horvath 1973, p. 336
71. Gray 2009, p.  9
72. Rayner-Canham 2011
73. Booth & Bloom 1972, p. 426; Cox 2004, pp. 17, 18, 27–8; Silberberg 2006, pp. 305–13
74. Cox 2004, pp. 17–18, 27–8; Silberberg 2006, p. 305–13
75. Rodgers 2011, pp. 232–3; 240–1
76. Roher 2001, pp. 4–6
77. Tyler 1948, p. 105; Reilly 2002, pp. 5–6
78. Hampel & Hawley 1976, p. 174
79. Goodrich 1844, p. 264; The Chemical News 1897, p. 189; Hampel & Hawley 1976, p. 191; Lewis 1993, p. 835; Hérold 2006, pp. 149–50
80. Oderberg 2007, p. 97
81. Brown & Holme 2006, p. 57
82. Wiberg 2001, p. 282; Simple Memory Art c. 2005
83. Chedd 1969, pp. 12–13
84. Kneen, Rogers & Simpson, 1972, p. 263. Columns 2 and 4 are sourced from this reference unless otherwise indicated.
85. Stoker 2010, p. 62; Chang 2002, p. 304. Chang speculates that the melting point of francium would be about 23 °C.
86. New Scientist 1975; Soverna 2004; Eichler et al. 2007; Austen 2012
87. Rochow 1966, p. 4
88. Hunt 2000, p. 256
89. McQuarrie & Rock 1987, p. 85
90. Desai, James & Ho 1984, p. 1160; Matula 1979, p. 1260
91. Choppin & Johnsen 1972, p. 351
92. Schaefer 1968, p. 76; Carapella 1968, p. 30
93. Kozyrev 1959, p. 104; Chizhikov & Shchastlivyi 1968, p. 25; Glazov, Chizhevskaya & Glagoleva 1969, p. 86
94. Bogoroditskii & Pasynkov 1967, p. 77; Jenkins & Kawamura 1976, p. 88
95. Hampel & Hawley 1976, p. 191; Wulfsberg 2000, p. 620
96. Swalin 1962, p. 216
97. Bailar et al. 1989, p. 742
98. Metcalfe, Williams & Castka 1974, p. 86
99. Chang 2002, p. 306
100. Pauling 1988, p. 183
101. Chedd 1969, pp. 24–5
102. Adler 1969, pp. 18–19
103. Hultgren 1966, p. 648; Young & Sessine 2000, p. 849; Bassett et al. 1966, p. 602
104. Rochow 1966, p. 4; Atkins et al. 2006, pp. 8, 122–3
105. Russell & Lee 2005, pp. 421, 423; Gray 2009, p. 23
106. Olmsted & Williams 1997, p. 975
107. Russell & Lee 2005, p. 401; Büchel, Moretto & Woditsch 2003, p. 278
108. Desch 1914, p. 86
109. Phillips & Williams 1965, p. 620
110. Van der Put 1998, p. 123
111. Klug & Brasted 1958, p. 199
112. Good et al. 1813
113. Sequeira 2011, p. 776
114. Gary 2013
115. Russell & Lee 2005, pp. 423–4; 405–6
116. Davidson & Lakin 1973, p. 627
117. Wiberg 2001, p. 589
118. Greenwood & Earnshaw 2002, p. 749; Schwartz 2002, p. 679
119. Antman 2001
120. Řezanka & Sigler 2008; Sekhon 2012
121. Emsley 2001, p. 67
122. Zhang et al. 2008, p. 360
123. Science Learning Hub 2009
124. Skinner et al. 1979; Tom, Elden & Marsh 2004, p. 135
125. Büchel 1983, p. 226
126. Emsley 2001, p. 391
127. Schauss 1991; Tao & Bolger 1997
128. Eagleson 1994, p. 450; EVM 2003, pp. 197‒202
129. Nielsen 1998
130. MacKenzie 2015, p. 36
131. Jaouen & Gibaud 2010
132. Smith et al. 2014
133. Stevens & Klarner, p. 205
134. Sneader 2005, pp. 57–59
135. Keall, Martin and Tunbridge 1946
136. Emsley 2001, p. 426
137. Oldfield et al. 1974, p. 65; Turner 2011
138. Ba et al. 2010; Daniel-Hoffmann, Sredni & Nitzan 2012; Molina-Quiroz et al. 2012
139. Peryea 1998
140. Hager 2006, p. 299
141. Apseloff 1999
142. Trivedi, Yung & Katz 2013, p. 209
143. Emsley 2001, p. 382; Burkhart, Burkhart & Morrell 2011
144. Thomas, Bialek & Hensel 2013, p. 1
145. Perry 2011, p. 74
146. UCR Today 2011; Wang & Robinson 2011; Kinjo et al. 2011
147. Kauthale et al. 2015
148. Gunn 2014, pp. 188, 191
149. Gupta, Mukherjee & Cameotra 1997, p. 280; Thomas & Visakh 2012, p. 99
150. Muncke 2013
151. Mokhatab & Poe 2012, p. 271
152. Craig, Eng & Jenkins 2003, p. 25
153. McKee 1984
154. Hai et al. 2012
155. Kohl & Nielsen 1997, pp. 699–700
156. Chopra et al. 2011
157. Le Bras, Wilkie & Bourbigot 2005, p. v
158. Wilkie & Morgan 2009, p. 187
159. Locke et al. 1956, p. 88
160. Carlin 2011, p. 6.2
161. Evans 1993, pp.  257–8
162. Corbridge 2013, p. 1149
163. Kaminow & Li 2002, p. 118
164. Deming 1925, pp. 330 (As₂O₃), 418 (B₂O₃; SiO₂; Sb₂O₃); Witt & Gatos 1968, p. 242 (GeO₂)
165. Eagleson 1994, p. 421 (GeO₂); Rothenberg 1976, 56, 118–19 (TeO₂)
166. Geckeler 1987, p. 20
167. Kreith & Goswami 2005, p. 12–109
168. Russell & Lee 2005, p. 397
169. Butterman & Jorgenson 2005, pp. 9–10
170. Shelby 2005, p. 43
171. Butterman & Carlin 2004, p. 22; Russell & Lee 2005, p. 422
172. Träger 2007, pp. 438, 958; Eranna 2011, p. 98
173. Rao 2002, p. 552; Löffler, Kündig & Dalla Torre 2007, p. 17–11
174. Guan et al. 2012; WPI-AIM 2012
175. Klement, Willens & Duwez 1960; Wanga, Dongb & Shek 2004, p. 45
176. Demetriou et al. 2011; Oliwenstein 2011
177. Karabulut et al. 2001, p. 15; Haynes 2012, p. 4–26
178. Schwartz 2002, pp. 679–680
179. Carter & Norton 2013, p. 403
180. Maeder 2013, pp. 3, 9–11
181. Tominaga 2006, p. 327–8; Chung 2010, p. 285–6; Kolobov & Tominaga 2012, p. 149
182. New Scientist 2014; Hosseini, Wright & Bhaskaran 2014; Farandos et al. 2014
183. Ordnance Office 1863, p. 293
184. Kosanke 2002, p. 110
185. Ellern 1968, pp. 246, 326–7
186. Conkling & Mocella 2010, p. 82
187. Crow 2011; Mainiero 2014
188. Schwab & Gerlach 1967; Yetter 2012, pp. 81; Lipscomb 1972, pp. 2–3, 5–6, 15
189. Ellern 1968, p. 135; Weingart 1947, p.  9
190. Conkling & Mocella 2010, p. 83
191. Conkling & Mocella 2010, pp. 181, 213
192. Ellern 1968, pp. 209–10; 322
193. Russell 2009, pp. 15, 17, 41, 79–80
194. Ellern 1968, p. 324
195. Ellern 1968, p. 328
196. Conkling & Mocella 2010, p. 171
197. Conkling & Mocella 2011, pp. 83–4
198. Berger 1997, p. 91; Hampel 1968, passim
199. Rochow 1966, p. 41; Berger 1997, pp. 42–3
200. Bomgardner 2013, p. 20
201. Russell & Lee 2005, p. 395; Brown et al. 2009, p. 489
202. Haller 2006, p. 4: "The study and understanding of the physics of semiconductors progressed slowly in the 19th and early 20th centuries ... Impurities and defects ... could not be controlled to the degree necessary to obtain reproducible results. This led influential physicists, including W. Pauli and I. Rabi, to comment derogatorily on the 'Physics of Dirt'."; Hoddeson 2007, pp. 25–34 (29)
203. Bianco et al. 2013
204. University of Limerick 2014; Kennedy et al. 2014
205. Lee et al. 2014
206. Russell & Lee 2005, pp. 421–2, 424
207. He et al. 2014
208. Berger 1997, p. 91
209. ScienceDaily 2012
210. Reardon 2005; Meskers, Hagelüken & Van Damme 2009, p. 1131
211. The Economist 2012
212. Whitten 2007, p. 488
213. Jaskula 2013
214. German Energy Society 2008, p. 43–44
215. Patel 2012, p. 248
216. Moore 2104; University of Utah 2014; Xu et al. 2014
217. Yang et al. 2012, p. 614
218. Moore 2010, p. 195
219. Moore 2011
220. Liu 2014
221. Bradley 2014; University of Utah 2014
222. Oxford English Dictionary 1989, 'metalloid'; Gordh, Gordh & Headrick 2003, p. 753
223. Foster 1936, pp. 212–13; Brownlee et al. 1943, p. 293
224. Calderazzo, Ercoli & Natta 1968, p. 257
225. Klemm 1950, pp. 133–42; Reilly 2004, p. 4
226. Walters 1982, pp. 32–3
227. Tyler 1948, p. 105
228. Foster & Wrigley 1958, p. 218: "The elements may be grouped into two classes: those that are metals and those that are nonmetals. There is also an intermediate group known variously as metalloids, meta-metals, semiconductors, or semimetals."
229. Slade 2006, p. 16
230. Corwin 2005, p. 80
231. Barsanov & Ginzburg 1974, p. 330
232. Bradbury et al. 1957, pp. 157, 659
233. Miller, Lee & Choe 2002, p. 21
234. King 2004, pp. 196–8; Ferro & Saccone 2008, p. 233
235. Pashaey & Seleznev 1973, p. 565; Gladyshev & Kovaleva 1998, p. 1445; Eason 2007, p. 294
236. Johansen & Mackintosh 1970, pp. 121–4; Divakar, Mohan & Singh 1984, p. 2337; Dávila et al. 2002, p. 035411-3
237. Jezequel & Thomas 1997, pp. 6620–6
238. Hindman 1968, p. 434: "The high values obtained for the [electrical] resistivity indicate that the metallic properties of neptunium are closer to the semimetals than the true metals. This is also true for other metals in the actinide series."; Dunlap et al. 1970, pp. 44, 46: "... α-Np is a semimetal, in which covalency effects are believed to also be of importance ... For a semimetal having strong covalent bonding, like α-Np ..."
239. Lister 1965, p. 54
240. Cotton et al. 1999, p. 502
241. Pinkerton 1800, p. 81
242. Goldsmith 1982, p. 526
243. Zhdanov 1965, pp. 74–5
244. Friend 1953, p. 68; IUPAC 1959, p. 10; IUPAC 1971, p. 11
245. IUPAC 2005; IUPAC 2006–
246. Van Setten et al. 2007, pp. 2460–1; Oganov et al. 2009, pp. 863–4
247. Housecroft & Sharpe 2008, p. 331; Oganov 2010, p. 212
248. Housecroft & Sharpe 2008, p. 333
249. Kross 2011
250. Berger 1997, p. 37
251. Greenwood & Earnshaw 2002, p. 144
252. Kopp, Lipták & Eren 2003, p. 221
253. Prudenziati 1977, p. 242
254. Berger 1997, pp. 87, 84
255. Mendeléeff 1897, p. 57
256. Rayner-Canham & Overton 2006, p. 291
257. Siekierski & Burgess 2002, p. 63
258. Wogan 2014
259. Siekierski & Burgess 2002, p. 86
260. Greenwood & Earnshaw 2002, p. 141; Henderson 2000, p. 58; Housecroft & Sharpe 2008, pp. 360–72
261. Parry et al. 1970, pp. 438, 448–51
262. Fehlner 1990, p. 202
263. Owen & Brooker 1991, p. 59; Wiberg 2001, p. 936
264. Greenwood & Earnshaw 2002, p. 145
265. Houghton 1979, p. 59
266. Fehlner 1990, pp. 205
267. Fehlner 1990, pp. 204–205, 207
268. Greenwood 2001, p. 2057
269. Salentine 1987, pp. 128–32; MacKay, MacKay & Henderson 2002, pp. 439–40; Kneen, Rogers & Simpson 1972, p. 394; Hiller & Herber 1960, inside front cover; p. 225
270. Sharp 1983, p. 56
271. Fokwa 2014, p. 10
272. Gillespie 1998
273. Haaland et al. 2000
274. Puddephatt & Monaghan 1989, p. 59
275. Mahan 1965, p. 485
276. Danaith 2008, p. 81.
277. Lidin 1996, p. 28
278. Kondrat'ev & Mel'nikova 1978
279. Holderness & Berry 1979, p. 111; Wiberg 2001, p. 980
280. Toy 1975, p. 506
281. Rao 2002, p. 22
282. Fehlner 1992, p. 1
283. Haiduc & Zuckerman 1985, p. 82
284. Greenwood & Earnshaw 2002, p. 331
285. Wiberg 2001, p. 824
286. Rochow 1973, p. 1337‒38
287. Russell & Lee 2005, p. 393
288. Zhang 2002, p. 70
289. Sacks 1998, p. 287
290. Rochow 1973, p. 1337, 1340
291. Allen & Ordway 1968, p. 152
292. Eagleson 1994, pp. 48, 127, 438, 1194; Massey 2000, p. 191
293. Orton 2004, p. 7. This is a typical value for high-purity silicon.
294. Coles & Caplin 1976, p. 106
295. Glazov, Chizhevskaya & Glagoleva 1969, pp. 59–63; Allen & Broughton 1987, p. 4967
296. Cotton, Wilkinson & Gaus 1995, p. 393
297. Wiberg 2001, p. 834
298. Partington 1944, p. 723
299. Cox 2004, p. 27
300. Hiller & Herber 1960, inside front cover; p. 225
301. Kneen, Rogers and Simpson 1972, p. 384
302. Bailar, Moeller & Kleinberg 1965, p. 513
303. Cotton, Wilkinson & Gaus 1995, pp. 319, 321
304. Smith 1990, p. 175
305. Poojary, Borade & Clearfield 1993
306. Wiberg 2001, pp. 851, 858
307. Barmett & Wilson 1959, p. 332
308. Powell 1988, p. 1
309. Greenwood & Earnshaw 2002, p. 371
310. Cusack 1967, p. 193
311. Russell & Lee 2005, pp. 399–400
312. Greenwood & Earnshaw 2002, p. 373
313. Moody 1991, p. 273
314. Russell & Lee 2005, p. 399
315. Berger 1997, pp. 71–2
316. Jolly 1966, pp. 125–6
317. Powell & Brewer 1938
318. Ladd 1999, p. 55
319. Everest 1953, p. 4120
320. Pan, Fu and Huang 1964, p. 182
321. Monconduit et al. 1992
322. Richens 1997, p. 152
323. Rupar et al. 2008
324. Schwietzer & Pesterfield 2010, pp. 190
325. Jolly & Latimer 1951, p. 2
326. Lidin 1996, p. 140
327. Ladd 1999, p. 56
328. Wiberg 2001, p. 896
329. Schwartz 2002, p. 269
330. Eggins 1972, p. 66; Wiberg 2001, p. 895
331. Greenwood & Earnshaw 2002, p. 383
332. Glockling 1969, p. 38; Wells 1984, p. 1175
333. Cooper 1968, pp. 28–9
334. Steele 1966, pp. 178, 188–9
335. Haller 2006, p. 3
336. See, for example, Walker & Tarn 1990, p. 590
337. Wiberg 2001, p. 742
338. Gray, Whitby & Mann 2011
339. Greenwood & Earnshaw 2002, p. 552
340. Parkes & Mellor 1943, p. 740
341. Russell & Lee 2005, p. 420
342. Carapella 1968, p. 30
343. Barfuß et al. 1981, p. 967
344. Greaves, Knights & Davis 1974, p. 369; Madelung 2004, pp. 405, 410
345. Bailar & Trotman-Dickenson 1973, p. 558; Li 1990
346. Bailar, Moeller & Kleinberg 1965, p. 477
347. Gillespie & Robinson 1963, p. 450
348. Paul et al. 1971; see also Ahmeda & Rucka 2011, pp. 2893, 2894
349. Gillespie & Passmore 1972, p. 478
350. Van Muylder & Pourbaix 1974, p. 521
351. Kolthoff & Elving 1978, p. 210
352. Moody 1991, p. 248–249
353. Cotton & Wilkinson 1999, pp. 396, 419
354. Eagleson 1994, p. 91
355. Massey 2000, p. 267
356. Timm 1944, p. 454
357. Partington 1944, p. 641; Kleinberg, Argersinger & Griswold 1960, p. 419
358. Morgan 1906, p. 163; Moeller 1954, p. 559
359. Corbridge 2013, pp. 122, 215
360. Douglade 1982
361. Zingaro 1994, p. 197; Emeléus & Sharpe 1959, p. 418; Addison & Sowerby 1972, p. 209; Mellor 1964, p. 337
362. Pourbaix 1974, p. 521; Eagleson 1994, p. 92; Greenwood & Earnshaw 2002, p. 572
363. Wiberg 2001, pp. 750, 975; Silberberg 2006, p. 314
364. Sidgwick 1950, p. 784; Moody 1991, pp. 248–9, 319
365. Krannich & Watkins 2006
366. Greenwood & Earnshaw 2002, p. 553
367. Dunstan 1968, p. 433
368. Parise 1996, p. 112
369. Carapella 1968a, p. 23
370. Moss 1952, pp. 174, 179
371. Dupree, Kirby & Freyland 1982, p. 604; Mhiaoui, Sar, & Gasser 2003
372. Kotz, Treichel & Weaver 2009, p. 62
373. Cotton et al. 1999, p. 396
374. King 1994, p. 174
375. Lidin 1996, p. 372
376. Lindsjö, Fischer & Kloo 2004
377. Friend 1953, p. 87
378. Fesquet 1872, pp. 109–14
379. Greenwood & Earnshaw 2002, p. 553; Massey 2000, p. 269
380. King 1994, p.171
381. Turova 2011, p. 46
382. Pourbaix 1974, p. 530
383. Wiberg 2001, p. 764
384. House 2008, p. 497
385. Mendeléeff 1897, p. 274
386. Emsley 2001, p. 428
387. Kudryavtsev 1974, p. 78
388. Bagnall 1966, pp. 32–3, 59, 137
389. Swink et al. 1966; Anderson et al. 1980
390. Ahmed, Fjellvåg & Kjekshus 2000
391. Chizhikov & Shchastlivyi 1970, p. 28
392. Kudryavtsev 1974, p. 77
393. Stuke 1974, p. 178; Donohue 1982, pp. 386–7; Cotton et al. 1999, p. 501
394. Becker, Johnson & Nussbaum 1971, p. 56
395. Berger 1997, p. 90
396. Chizhikov & Shchastlivyi 1970, p. 16
397. Jolly 1966, pp. 66–7
398. Schwietzer & Pesterfield 2010, p. 239
399. Cotton et al. 1999, p. 498
400. Wells 1984, p. 715
401. Wiberg 2001, p. 588
402. Mellor 1964a, p.  30; Wiberg 2001, p. 589
403. Greenwood & Earnshaw 2002, p. 765–6
404. Bagnall 1966, p. 134–51; Greenwood & Earnshaw 2002, p. 786
405. Detty & O'Regan 1994, pp. 1–2
406. Hill & Holman 2000, p. 124
407. Chang 2002, p. 314
408. Kent 1950, pp. 1–2; Clark 1960, p. 588; Warren & Geballe 1981
409. Housecroft & Sharpe 2008, p. 384; IUPAC 2006–, rhombohedral graphite entry
410. Mingos 1998, p. 171
411. Wiberg 2001, p. 781
412. Charlier, Gonze & Michenaud 1994
413. Atkins et al. 2006, pp. 320–1
414. Savvatimskiy 2005, p. 1138
415. Togaya 2000
416. Savvatimskiy 2009
417. Inagaki 2000, p. 216; Yasuda et al. 2003, pp. 3–11
418. O'Hare 1997, p. 230
419. Traynham 1989, pp. 930–1; Prakash & Schleyer 1997
420. Olmsted & Williams 1997, p. 436
421. Bailar et al. 1989, p. 743
422. Moore et al. 1985
423. House & House 2010, p. 526
424. Wiberg 2001, p. 798
425. Eagleson 1994, p. 175
426. Atkins et al. 2006, p. 121
427. Russell & Lee 2005, pp. 358–9
428. Keevil 1989, p. 103
429. Russell & Lee 2005, pp. 358–60 et seq
430. Harding, Janes & Johnson 2002, pp. 118
431. Metcalfe, Williams & Castka 1974, p. 539
432. Cobb & Fetterolf 2005, p. 64; Metcalfe, Williams & Castka 1974, p. 539
433. Ogata, Li & Yip 2002; Boyer et al. 2004, p. 1023; Russell & Lee 2005, p. 359
434. Cooper 1968, p. 25; Henderson 2000, p. 5; Silberberg 2006, p. 314
435. Wiberg 2001, p. 1014
436. Daub & Seese 1996, pp. 70, 109: "Aluminum is not a metalloid but a metal because it has mostly metallic properties."; Denniston, Topping & Caret 2004, p. 57: "Note that aluminum (Al) is classified as a metal, not a metalloid."; Hasan 2009, p. 16: "Aluminum does not have the characteristics of a metalloid but rather those of a metal."
437. Holt, Rinehart & Wilson c. 2007
438. Tuthill 2011
439. Stott 1956, p. 100
440. Steele 1966, p. 60
441. Moody 1991, p. 303
442. Emsley 2001, p. 382
443. Young et al. 2010, p. 9; Craig & Maher 2003, p. 391. Selenium is "near metalloidal".
444. Rochow 1957
445. Rochow 1966, p. 224
446. Moss 1952, p. 192
447. Glinka 1965, p. 356
448. Evans 1966, pp. 124–5
449. Regnault 1853, p. 208
450. Scott & Kanda 1962, p. 311
451. Cotton et al. 1999, pp. 496, 503–4
452. Arlman 1939; Bagnall 1966, pp. 135, 142–3
453. Chao & Stenger 1964
454. Berger 1997, pp. 86–7
455. Snyder 1966, p. 242
456. Fritz & Gjerde 2008, p. 235
457. Meyer et al. 2005, p. 284; Manahan 2001, p. 911; Szpunar et al. 2004, p. 17
458. US Environmental Protection Agency 1988, p. 1; Uden 2005, pp. 347‒8
459. De Zuane 1997, p. 93; Dev 2008, pp. 2‒3
460. Wiberg 2001, p. 594
461. Greenwood & Earnshaw 2002, p. 786; Schwietzer & Pesterfield 2010, pp. 242–3
462. Bagnall 1966, p. 41; Nickless 1968, p. 79
463. Bagnall 1990, pp. 313–14; Lehto & Hou 2011, p. 220; Siekierski & Burgess 2002, p. 117: "The tendency to form X²⁻ anions decreases down the Group [16 elements] ..."
464. Legit, Friák & Šob 2010, p. 214118-18
465. Manson & Halford 2006, pp. 378, 410
466. Bagnall 1957, p. 62; Fernelius 1982, p. 741
467. Bagnall 1966, p. 41; Barrett 2003, p. 119
468. Hawkes 2010; Holt, Rinehart & Wilson c. 2007; Hawkes 1999, p. 14; Roza 2009, p. 12
469. Keller 1985
470. Harding, Johnson & Janes 2002, p. 61
471. Long & Hentz 1986, p. 58
472. Vasáros & Berei 1985, p. 109
473. Haissinsky & Coche 1949, p. 400
474. Brownlee et al. 1950, p. 173
475. Hermann, Hoffmann & Ashcroft 2013
476. Siekierski & Burgess 2002, pp. 65, 122
477. Emsley 2001, p. 48
478. Rao & Ganguly 1986
479. Krishnan et al. 1998
480. Glorieux, Saboungi & Enderby 2001
481. Millot et al. 2002
482. Vasáros & Berei 1985, p. 117
483. Kaye & Laby 1973, p. 228
484. Samsonov 1968, p. 590
485. Korenman 1959, p. 1368
486. Rossler 1985, pp. 143–4
487. Champion et al. 2010
488. Borst 1982, pp. 465, 473
489. Batsanov 1971, p. 811
490. Swalin 1962, p. 216; Feng & Lin 2005, p. 157
491. Schwietzer & Pesterfield 2010, pp. 258–60
492. Hawkes 1999, p. 14
493. Olmsted & Williams 1997, p. 328; Daintith 2004, p. 277
494. Eberle1985, pp. 213–16, 222–7
495. Restrepo et al. 2004, p. 69; Restrepo et al. 2006, p. 411
496. Greenwood & Earnshaw 2002, p. 804
497. Greenwood & Earnshaw 2002, p. 803
498. Wiberg 2001, p. 416
499. Craig & Maher 2003, p. 391; Schroers 2013, p. 32; Vernon 2013, pp. 1704–1705
500. Cotton et al. 1999, p. 42
501. Marezio & Licci 2000, p. 11
502. Vernon 2013, p. 1705
503. Russell & Lee 2005, p. 5
504. Parish 1977, pp. 178, 192–3
505. Eggins 1972, p. 66; Rayner-Canham & Overton 2006, pp. 29–30
506. Atkins et al. 2006, pp. 320–1; Bailar et al. 1989, p. 742–3
507. Rochow 1966, p. 7; Taniguchi et al. 1984, p. 867: "... black phosphorus ... [is] characterized by the wide valence bands with rather delocalized nature."; Morita 1986, p. 230; Carmalt & Norman 1998, p. 7: "Phosphorus ... should therefore be expected to have some metalloid properties."; Du et al. 2010. Interlayer interactions in black phosphorus, which are attributed to van der Waals-Keesom forces, are thought to contribute to the smaller band gap of the bulk material (calculated 0.19 eV; observed 0.3 eV) as opposed to the larger band gap of a single layer (calculated ~0.75 eV).
508. Stuke 1974, p. 178; Cotton et al. 1999, p. 501; Craig & Maher 2003, p. 391
509. Steudel 1977, p. 240: "... considerable orbital overlap must exist, to form intermolecular, many-center ... [sigma] bonds, spread through the layer and populated with delocalized electrons, reflected in the properties of iodine (lustre, color, moderate electrical conductivity)."; Segal 1989, p. 481: "Iodine exhibits some metallic properties ..."
510. Lutz et al. 2011, p. 17
511. Yacobi & Holt 1990, p. 10; Wiberg 2001, p. 160
512. Greenwood & Earnshaw 2002, pp. 479, 482
513. Eagleson 1994, p. 820
514. Oxtoby, Gillis & Campion 2008, p. 508
515. Brescia et al. 1980, pp. 166–71
516. Fine & Beall 1990, p. 578
517. Wiberg 2001, p. 901
518. Berger 1997, p. 80
519. Lovett 1977, p. 101
520. Cohen & Chelikowsky 1988, p. 99
521. Taguena-Martinez, Barrio & Chambouleyron 1991, p. 141
522. Ebbing & Gammon 2010, p. 891
523. Asmussen & Reinhard 2002, p. 7
524. Deprez & McLachan 1988
525. Addison 1964 (P, Se, Sn); Marković, Christiansen & Goldman 1998 (Bi); Nagao et al. 2004
526. Lide 2005; Wiberg 2001, p. 423: At
527. Cox 1997, pp. 182‒86
528. MacKay, MacKay & Henderson 2002, p. 204
529. Baudis 2012, pp. 207–8
530. Wiberg 2001, p. 741
531. Chizhikov & Shchastlivyi 1968, p. 96
532. Greenwood & Earnshaw 2002, pp. 140–1, 330, 369, 548–9, 749: B, Si, Ge, As, Sb, Te
533. Kudryavtsev 1974, p. 158
534. Greenwood & Earnshaw 2002, pp. 271, 219, 748–9, 886: C, Al, Se, Po, At; Wiberg 2001, p. 573: Se
535. United Nuclear 2013
536. Zalutsky & Pruszynski 2011, p. 181

Bibliography

• Addison WE 1964, The Allotropy of the Elements, Oldbourne Press, London
• Addison CC & Sowerby DB 1972, Main Group Elements: Groups V and VI, Butterworths, London, ISBN 0-8391-1005-7
• Adler D 1969, 'Half-way Elements: The Technology of Metalloids', book review, Technology Review, vol. 72, no. 1, Oct/Nov, pp. 18–19, ISSN 0040-1692
• Ahmed MAK, Fjellvåg H & Kjekshus A 2000, 'Synthesis, Structure and Thermal Stability of Tellurium Oxides and Oxide Sulfate Formed from Reactions in Refluxing Sulfuric Acid', Journal of the Chemical Society, Dalton Transactions, no. 24, pp. 4542–9, doi:10.1039/B005688J
• Ahmeda E & Rucka M 2011, 'Homo- and heteroatomic polycations of groups 15 and 16. Recent advances in synthesis and isolation using room temperature ionic liquids', Coordination Chemistry Reviews, vol. 255, nos 23–24, pp. 2892–2903, doi:10.1016/j.ccr.2011.06.011
• Allen DS & Ordway RJ 1968, Physical Science, 2nd ed., Van Nostrand, Princeton, New Jersey, ISBN 978-0-442-00290-9
• Allen PB & Broughton JQ 1987, 'Electrical Conductivity and Electronic Properties of Liquid Silicon', Journal of Physical Chemistry, vol. 91, no. 19, pp. 4964–70, doi:10.1021/j100303a015
• Alloul H 2010, Introduction to the Physics of Electrons in Solids, Springer-Verlag, Berlin, ISBN 3-642-13564-1
• Anderson JB, Rapposch MH, Anderson CP & Kostiner E 1980, 'Crystal Structure Refinement of Basic Tellurium Nitrate: A Reformulation as (Te₂O₄H)⁺(NO₃)⁻', Monatshefte für Chemie/ Chemical Monthly, vol. 111, no. 4, pp. 789–96, doi:10.1007/BF00899243
• Antman KH 2001, 'Introduction: The History of Arsenic Trioxide in Cancer Therapy', The Oncologist, vol. 6, suppl. 2, pp. 1–2, doi:10.1634/theoncologist.6-suppl_2-1
• Apseloff G 1999, 'Therapeutic Uses of Gallium Nitrate: Past, Present, and Future', American Journal of Therapeutics, vol. 6, no. 6, pp. 327–39, ISSN 1536-3686
• Arlman EJ 1939, 'The Complex Compounds P(OH)₄.ClO₄ and Se(OH)₃.ClO₄', Recueil des Travaux Chimiques des Pays-Bas, vol. 58, no. 10, pp. 871–4, ISSN 0165-0513
• Askeland DR, Phulé PP & Wright JW 2011, The Science and Engineering of Materials, 6th ed., Cengage Learning, Stamford, CT, ISBN 0-495-66802-8
• Asmussen J & Reinhard DK 2002, Diamond Films Handbook, Marcel Dekker, New York, ISBN 0-8247-9577-6
• Atkins P, Overton T, Rourke J, Weller M & Armstrong F 2006, Shriver & Atkins' Inorganic Chemistry, 4th ed., Oxford University Press, Oxford, ISBN 0-7167-4878-9
• Atkins P, Overton T, Rourke J, Weller M & Armstrong F 2010, Shriver & Atkins' Inorganic Chemistry, 5th ed., Oxford University Press, Oxford, ISBN 1-4292-1820-7
• Austen K 2012, 'A Factory for Elements that Barely Exist', New Scientist, 21 Apr, p. 12
• Ba LA, Döring M, Jamier V & Jacob C 2010, 'Tellurium: an Element with Great Biological Potency and Potential', Organic & Biomolecular Chemistry, vol. 8, pp. 4203–16, doi:10.1039/C0OB00086H
• Bagnall KW 1957, Chemistry of the Rare Radioelements: Polonium-actinium, Butterworths Scientific Publications, London
• Bagnall KW 1966, The Chemistry of Selenium, Tellurium and Polonium, Elsevier, Amsterdam
• Bagnall KW 1990, 'Compounds of Polonium', in KC Buschbeck & C Keller (eds), Gmelin Handbook of Inorganic and Organometallic Chemistry, 8th ed., Po Polonium, Supplement vol. 1, Springer-Verlag, Berlin, pp. 285–340, ISBN 3-540-93616-5
• Bailar JC, Moeller T & Kleinberg J 1965, University Chemistry, DC Heath, Boston
• Bailar JC & Trotman-Dickenson AF 1973, Comprehensive Inorganic Chemistry, vol. 4, Pergamon, Oxford
• Bailar JC, Moeller T, Kleinberg J, Guss CO, Castellion ME & Metz C 1989, Chemistry, 3rd ed., Harcourt Brace Jovanovich, San Diego, ISBN 0-15-506456-8
• Barfuß H, Böhnlein G, Freunek P, Hofmann R, Hohenstein H, Kreische W, Niedrig H and Reimer A 1981, 'The Electric Quadrupole Interaction of ¹¹¹Cd in Arsenic Metal and in the System Sb_1–xIn_x and Sb_1–xCd_x', Hyperfine Interactions, vol. 10, nos 1–4, pp. 967–72, doi:10.1007/BF01022038
• Barnett EdB & Wilson CL 1959, Inorganic Chemistry: A Text-book for Advanced Students, 2nd ed., Longmans, London
• Barrett J 2003, Inorganic Chemistry in Aqueous Solution, The Royal Society of Chemistry, Cambridge, ISBN 0-85404-471-X
• Barsanov GP & Ginzburg AI 1974, 'Mineral', in AM Prokhorov (ed.), Great Soviet Encyclopedia, 3rd ed., vol. 16, Macmillan, New York, pp. 329–32
• Bassett LG, Bunce SC, Carter AE, Clark HM & Hollinger HB 1966, Principles of Chemistry, Prentice-Hall, Englewood Cliffs, New Jersey
• Batsanov SS 1971, 'Quantitative Characteristics of Bond Metallicity in Crystals', Journal of Structural Chemistry, vol. 12, no. 5, pp. 809–13, doi:10.1007/BF00743349
• Baudis U & Fichte R 2012, 'Boron and Boron Alloys', in F Ullmann (ed.), Ullmann's Encyclopedia of Industrial Chemistry, vol. 6, Wiley-VCH, Weinheim, pp. 205–17, doi:10.1002/14356007.a04_281
• Becker WM, Johnson VA & Nussbaum 1971, 'The Physical Properties of Tellurium', in WC Cooper (ed.), Tellurium, Van Nostrand Reinhold, New York
• Belpassi L, Tarantelli F, Sgamellotti A & Quiney HM 2006, 'The Electronic Structure of Alkali Aurides. A Four-Component Dirac−Kohn−Sham study', The Journal of Physical Chemistry A, vol. 110, no. 13, April 6, pp. 4543–54, doi:10.1021/jp054938w
• Berger LI 1997, Semiconductor Materials, CRC Press, Boca Raton, Florida, ISBN 0-8493-8912-7
• Bettelheim F, Brown WH, Campbell MK & Farrell SO 2010, Introduction to General, Organic, and Biochemistry, 9th ed., Brooks/Cole, Belmont CA, ISBN 0-495-39112-3
• Bianco E, Butler S, Jiang S, Restrepo OD, Windl W & Goldberger JE 2013, 'Stability and Exfoliation of Germanane: A Germanium Graphane Analogue,' ACS Nano, March 19 (web), doi:10.1021/nn4009406
• Bodner GM & Pardue HL 1993, Chemistry, An Experimental Science, John Wiley & Sons, New York, ISBN 0-471-59386-9
• Bogoroditskii NP & Pasynkov VV 1967, Radio and Electronic Materials, Iliffe Books, London
• Bomgardner MM 2013, 'Thin-Film Solar Firms Revamp To Stay In The Game', Chemical & Engineering News, vol. 91, no. 20, pp. 20–1, ISSN 0009-2347
• Bond GC 2005, Metal-Catalysed Reactions of Hydrocarbons, Springer, New York, ISBN 0-387-24141-8
• Booth VH & Bloom ML 1972, Physical Science: A Study of Matter and Energy, Macmillan, New York
• Borst KE 1982, 'Characteristic Properties of Metallic Crystals', Journal of Educational Modules for Materials Science and Engineering, vol. 4, no. 3, pp. 457–92, ISSN 0197-3940
• Boyer RD, Li J, Ogata S & Yip S 2004, 'Analysis of Shear Deformations in Al and Cu: Empirical Potentials Versus Density Functional Theory', Modelling and Simulation in Materials Science and Engineering, vol. 12, no. 5, pp. 1017–29, doi:10.1088/0965-0393/12/5/017
• Bradbury GM, McGill MV, Smith HR & Baker PS 1957, Chemistry and You, Lyons and Carnahan, Chicago
• Bradley D 2014, Resistance is Low: New Quantum Effect, spectroscopyNOW, viewed 15 December 2014-12-15
• Brescia F, Arents J, Meislich H & Turk A 1980, Fundamentals of Chemistry, 4th ed., Academic Press, New York, ISBN 0-12-132392-7
• Brown L & Holme T 2006, Chemistry for Engineering Students, Thomson Brooks/Cole, Belmont California, ISBN 0-495-01718-3
• Brown WP c. 2007 'The Properties of Semi-Metals or Metalloids,' Doc Brown's Chemistry: Introduction to the Periodic Table, viewed 8 February 2013
• Brown TL, LeMay HE, Bursten BE, Murphy CJ, Woodward P 2009, Chemistry: The Central Science, 11th ed., Pearson Education, Upper Saddle River, New Jersey, ISBN 978-0-13-235848-4
• Brownlee RB, Fuller RW, Hancock WJ, Sohon MD & Whitsit JE 1943, Elements of Chemistry, Allyn and Bacon, Boston
• Brownlee RB, Fuller RT, Whitsit JE Hancock WJ & Sohon MD 1950, Elements of Chemistry, Allyn and Bacon, Boston
• Bucat RB (ed.) 1983, Elements of Chemistry: Earth, Air, Fire & Water, vol. 1, Australian Academy of Science, Canberra, ISBN 0-85847-113-2
• Büchel KH (ed.) 1983, Chemistry of Pesticides, John Wiley & Sons, New York, ISBN 0-471-05682-0
• Büchel KH, Moretto H-H, Woditsch P 2003, Industrial Inorganic Chemistry, 2nd ed., Wiley-VCH, ISBN 3-527-29849-5
• Burkhart CN, Burkhart CG & Morrell DS 2011, 'Treatment of Tinea Versicolor', in HI Maibach & F Gorouhi (eds), Evidence Based Dermatology, 2nd ed., People's Medical Publishing House-USA, Shelton, CT, pp. 365–72, ISBN 978-1-60795-039-4
• Burrows A, Holman J, Parsons A, Pilling G & Price G 2009, Chemistry³: Introducing Inorganic, Organic and Physical Chemistry, Oxford University, Oxford, ISBN 0-19-927789-3
• Butterman WC & Carlin JF 2004, Mineral Commodity Profiles: Antimony, US Geological Survey
• Butterman WC & Jorgenson JD 2005, Mineral Commodity Profiles: Germanium, US Geological Survey
• Calderazzo F, Ercoli R & Natta G 1968, 'Metal Carbonyls: Preparation, Structure, and Properties', in I Wender & P Pino (eds), Organic Syntheses via Metal Carbonyls: Volume 1, Interscience Publishers, New York, pp. 1–272
• Carapella SC 1968a, 'Arsenic' in CA Hampel (ed.), The Encyclopedia of the Chemical Elements, Reinhold, New York, pp. 29–32
• Carapella SC 1968, 'Antimony' in CA Hampel (ed.), The Encyclopedia of the Chemical Elements, Reinhold, New York, pp. 22–5
• Carlin JF 2011, Minerals Year Book: Antimony, United States Geological Survey
• Carmalt CJ & Norman NC 1998, 'Arsenic, Antimony and Bismuth: Some General Properties and Aspects of Periodicity', in NC Norman (ed.), Chemistry of Arsenic, Antimony and Bismuth, Blackie Academic & Professional, London, pp. 1–38, ISBN 0-7514-0389-X
• Carter CB & Norton MG 2013, Ceramic Materials: Science and Engineering, 2nd ed., Springer Science+Business Media, New York, ISBN 978-1-4614-3523-5
• Cegielski C 1998, Yearbook of Science and the Future, Encyclopædia Britannica, Chicago, ISBN 0-85229-657-6
• Chalmers B 1959, Physical Metallurgy, John Wiley & Sons, New York
• Champion J, Alliot C, Renault E, Mokili BM, Chérel M, Galland N & Montavon G 2010, 'Astatine Standard Redox Potentials and Speciation in Acidic Medium', The Journal of Physical Chemistry A, vol. 114, no. 1, pp. 576–82, doi:10.1021/jp9077008
• Chang R 2002, Chemistry, 7th ed., McGraw Hill, Boston, ISBN 0-07-246533-6
• Chao MS & Stenger VA 1964, 'Some Physical Properties of Highly Purified Bromine', Talanta, vol. 11, no. 2, pp. 271–81, doi:10.1016/0039-9140(64)80036-9
• Charlier J-C, Gonze X, Michenaud J-P 1994, First-principles Study of the Stacking Effect on the Electronic Properties of Graphite(s), Carbon, vol. 32, no. 2, pp. 289–99, doi:10.1016/0008-6223(94)90192-9
• Chatt J 1951, 'Metal and Metalloid Compounds of the Alkyl Radicals', in EH Rodd (ed.), Chemistry of Carbon Compounds: A Modern Comprehensive Treatise, vol. 1, part A, Elsevier, Amsterdam, pp. 417–58
• Chedd G 1969, Half-Way Elements: The Technology of Metalloids, Doubleday, New York
• Chizhikov DM & Shchastlivyi VP 1968, Selenium and Selenides, translated from the Russian by EM Elkin, Collet's, London
• Chizhikov DM & Shchastlivyi 1970, Tellurium and the Tellurides, Collet's, London
• Choppin GR & Johnsen RH 1972, Introductory Chemistry, Addison-Wesley, Reading, Massachusetts
• Chopra IS, Chaudhuri S, Veyan JF & Chabal YJ 2011, 'Turning Aluminium into a Noble-metal-like Catalyst for Low-temperature Activation of Molecular Hydrogen', Nature Materials, vol. 10, pp. 884–889, doi:10.1038/nmat3123
• Chung DDL 2010, Composite Materials: Science and Applications, 2nd ed., Springer-Verlag, London, ISBN 978-1-84882-830-8
• Clark GL 1960, The Encyclopedia of Chemistry, Reinhold, New York
• Cobb C & Fetterolf ML 2005, The Joy of Chemistry, Prometheus Books, New York, ISBN 1-59102-231-2
• Cohen ML & Chelikowsky JR 1988, Electronic Structure and Optical Properties of Semiconductors, Springer Verlag, Berlin, ISBN 3-540-18818-5
• Coles BR & Caplin AD 1976, The Electronic Structures of Solids, Edward Arnold, London, ISBN 0-8448-0874-1
• Conkling JA & Mocella C 2011, Chemistry of Pyrotechnics: Basic Principles and Theory, 2nd ed., CRC Press, Boca Raton, FL, ISBN 978-1-57444-740-8
• Considine DM & Considine GD (eds) 1984, 'Metalloid', in Van Nostrand Reinhold Encyclopedia of Chemistry, 4th ed., Van Nostrand Reinhold, New York, ISBN 0-442-22572-5
• Cooper DG 1968, The Periodic Table, 4th ed., Butterworths, London
• Corbridge DEC 2013, Phosphorus: Chemistry, Biochemistry and Technology, 6th ed., CRC Press, Boca Raton, Florida, ISBN 978-1-4398-4088-7
• Corwin CH 2005, Introductory Chemistry: Concepts & Connections, 4th ed., Prentice Hall, Upper Saddle River, New Jersey, ISBN 0-13-144850-1
• Cotton FA, Wilkinson G & Gaus P 1995, Basic Inorganic Chemistry, 3rd ed., John Wiley & Sons, New York, ISBN 0-471-50532-3
• Cotton FA, Wilkinson G, Murillo CA & Bochmann 1999, Advanced Inorganic Chemistry, 6th ed., John Wiley & Sons, New York, ISBN 0-471-19957-5
• Cox PA 1997, The Elements: Their Origin, Abundance and Distribution, Oxford University, Oxford, ISBN 0-19-855298-X
• Cox PA 2004, Inorganic Chemistry, 2nd ed., Instant Notes series, Bios Scientific, London, ISBN 1-85996-289-0
• Craig PJ, Eng G & Jenkins RO 2003, 'Occurrence and Pathways of Organometallic Compounds in the Environment—General Considerations' in PJ Craig (ed.), Organometallic Compounds in the Environment, 2nd ed., John Wiley & Sons, Chichester, West Sussex, pp. 1–56, ISBN 0471899933
• Craig PJ & Maher WA 2003, 'Organoselenium compounds in the environment', in Organometallic Compounds in the Environment, PJ Craig (ed.), John Wiley & Sons, New York, pp. 391–398, ISBN 0-471-89993-3
• Crow JM 2011, 'Boron Carbide Could Light Way to Less-toxic Green Pyrotechnics', Nature News, 8 April, doi:10.1038/news.2011.222
• Cusack N 1967, The Electrical and Magnetic Properties of Solids: An Introductory Textbook, 5th ed., John Wiley & Sons, New York
• Cusack N E 1987, The Physics of Structurally Disordered Matter: An Introduction, A Hilger in association with the University of Sussex Press, Bristol, ISBN 0-85274-591-5
• Daintith J (ed.) 2004, Oxford Dictionary of Chemistry, 5th ed., Oxford University, Oxford, ISBN 0-19-920463-2
• Danaith J (ed.) 2008, Oxford Dictionary of Chemistry, Oxford University Press, Oxford, ISBN 978-0-19-920463-2
• Daniel-Hoffmann M, Sredni B & Nitzan Y 2012, 'Bactericidal Activity of the Organo-Tellurium Compound AS101 Against Enterobacter Cloacae,' Journal of Antimicrobial Chemotherapy, vol. 67, no. 9, pp. 2165–72, doi:10.1093/jac/dks185
• Daub GW & Seese WS 1996, Basic Chemistry, 7th ed., Prentice Hall, New York, ISBN 0-13-373630-X
• Davidson DF & Lakin HW 1973, 'Tellurium', in DA Brobst & WP Pratt (eds), United States Mineral Resources, Geological survey professional paper 820, United States Government Printing Office, Washington, pp. 627–30
• Dávila ME, Molotov SL, Laubschat C & Asensio MC 2002, 'Structural Determination of Yb Single-Crystal Films Grown on W(110) Using Photoelectron Diffraction', Physical Review B, vol. 66, no. 3, p. 035411–18, doi:10.1103/PhysRevB.66.035411
• Demetriou MD, Launey ME, Garrett G, Schramm JP, Hofmann DC, Johnson WL & Ritchie RO 2011, 'A Damage-Tolerant Glass', Nature Materials, vol. 10, February, pp. 123–8, doi:10.1038/nmat2930
• Deming HG 1925, General Chemistry: An Elementary Survey, 2nd ed., John Wiley & Sons, New York
• Denniston KJ, Topping JJ & Caret RL 2004, General, Organic, and Biochemistry, 5th ed., McGraw-Hill, New York, ISBN 0-07-282847-1
• Deprez N & McLachan DS 1988, 'The Analysis of the Electrical Conductivity of Graphite Conductivity of Graphite Powders During Compaction', Journal of Physics D: Applied Physics, vol. 21, no. 1, doi:10.1088/0022-3727/21/1/015
• Desai PD, James HM & Ho CY 1984, 'Electrical Resistivity of Aluminum and Manganese', Journal of Physical and Chemical Reference Data, vol. 13, no. 4, pp. 1131–72, doi:10.1063/1.555725
• Desch CH 1914, Intermetallic Compounds, Longmans, Green and Co., New York
• Detty MR & O'Regan MB 1994, Tellurium-Containing Heterocycles, (The Chemistry of Heterocyclic Compounds, vol. 53), John Wiley & Sons, New York
• Dev N 2008, 'Modelling Selenium Fate and Transport in Great Salt Lake Wetlands', PhD dissertation, University of Utah, ProQuest, Ann Arbor, Michigan, ISBN 0-549-86542-X
• De Zuane J 1997, Handbook of Drinking Water Quality, 2nd ed., John Wiley & Sons, New York, ISBN 0-471-28789-X
• Di Pietro P 2014, Optical Properties of Bismuth-Based Topological Insulators, Springer International Publishing, Cham, Switzerland, ISBN 978-3-319-01990-1
• Divakar C, Mohan M & Singh AK 1984, 'The Kinetics of Pressure-Induced Fcc-Bcc Transformation in Ytterbium', Journal of Applied Physics, vol. 56, no. 8, pp. 2337–40, doi:10.1063/1.334270
• Donohue J 1982, The Structures of the Elements, Robert E. Krieger, Malabar, Florida, ISBN 0-89874-230-7
• Douglade J & Mercier R 1982, 'Structure Cristalline et Covalence des Liaisons dans le Sulfate d'Arsenic(III), As₂(SO₄)₃', Acta Crystallographica Section B, vol. 38, no. 3, pp. 720–3, doi:10.1107/S056774088200394X
• Du Y, Ouyang C, Shi S & Lei M 2010, 'Ab Initio Studies on Atomic and Electronic Structures of Black Phosphorus', Journal of Applied Physics, vol. 107, no. 9, pp. 093718–1–4, doi:10.1063/1.3386509
• Dunlap BD, Brodsky MB, Shenoy GK & Kalvius GM 1970, 'Hyperfine Interactions and Anisotropic Lattice Vibrations of ²³⁷Np in α-Np Metal', Physical Review B, vol. 1, no. 1, pp. 44–9, doi:10.1103/PhysRevB.1.44
• Dunstan S 1968, Principles of Chemistry, D. Van Nostrand Company, London
• Dupree R, Kirby DJ & Freyland W 1982, 'N.M.R. Study of Changes in Bonding and the Metal-Non-metal Transition in Liquid Caesium-Antimony Alloys', Philosophical Magazine Part B, vol. 46 no. 6, pp. 595–606, doi:10.1080/01418638208223546
• Eagleson M 1994, Concise Encyclopedia Chemistry, Walter de Gruyter, Berlin, ISBN 3-11-011451-8
• Eason R 2007, Pulsed Laser Deposition of Thin Films: Applications-Led Growth of Functional Materials, Wiley-Interscience, New York
• Ebbing DD & Gammon SD 2010, General Chemistry, 9th ed. enhanced, Brooks/Cole, Belmont, California, ISBN 978-0-618-93469-0
• Eberle SH 1985, 'Chemical Behavior and Compounds of Astatine', pp. 183–209, in Kugler & Keller
• Edwards PP & Sienko MJ 1983, 'On the Occurrence of Metallic Character in the Periodic Table of the Elements', Journal of Chemical Education, vol. 60, no. 9, pp. 691–6, doi:10.1021ed060p691
• Edwards PP 1999, 'Chemically Engineering the Metallic, Insulating and Superconducting State of Matter' in KR Seddon & M Zaworotko (eds), Crystal Engineering: The Design and Application of Functional Solids, Kluwer Academic, Dordrecht, pp. 409–431, ISBN 0-7923-5905-4
• Edwards PP 2000, 'What, Why and When is a metal?', in N Hall (ed.), The New Chemistry, Cambridge University, Cambridge, pp. 85–114, ISBN 0-521-45224-4
• Edwards PP, Lodge MTJ, Hensel F & Redmer R 2010, '... A Metal Conducts and a Non-metal Doesn't', Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 368, pp. 941–65, doi:10.1098/rsta.2009.0282
• Eggins BR 1972, Chemical Structure and Reactivity, MacMillan, London, ISBN 0-333-08145-5
• Eichler R, Aksenov NV, Belozerov AV, Bozhikov GA, Chepigin VI, Dmitriev SN, Dressler R, Gäggeler HW, Gorshkov VA, Haenssler F, Itkis MG, Laube A, Lebedev VY, Malyshev ON, Oganessian YT, Petrushkin OV, Piguet D, Rasmussen P, Shishkin SV, Shutov, AV, Svirikhin AI, Tereshatov EE, Vostokin GK, Wegrzecki M & Yeremin AV 2007, 'Chemical Characterization of Element 112,' Nature, vol. 447, pp. 72–5, doi:10.1038/nature05761
• Ellern H 1968, Military and Civilian Pyrotechnics, Chemical Publishing Company, New York
• Emeléus HJ & Sharpe AG 1959, Advances in Inorganic Chemistry and Radiochemistry, vol. 1, Academic Press, New York
• Emsley J 1971, The Inorganic Chemistry of the Non-metals, Methuen Educational, London, ISBN 0-423-86120-4
• Emsley J 2001, Nature's Building Blocks: An A–Z guide to the Elements, Oxford University Press, Oxford, ISBN 0-19-850341-5
• Eranna G 2011, Metal Oxide Nanostructures as Gas Sensing Devices, Taylor & Francis, Boca Raton, Florida, ISBN 1-4398-6340-7
• Evans KA 1993, 'Properties and Uses of Oxides and Hydroxides,' in AJ Downs (ed.), Chemistry of Aluminium, Gallium, Indium, and Thallium, Blackie Academic & Professional, Bishopbriggs, Glasgow, pp. 248–91, ISBN 0-7514-0103-X
• Evans RC 1966, An Introduction to Crystal Chemistry, Cambridge University, Cambridge
• Everest DA 1953, 'The Chemistry of Bivalent Germanium Compounds. Part IV. Formation of Germanous Salts by Reduction with Hydrophosphorous Acid.' Journal of the Chemical Society, pp. 4117–4120, doi:10.1039/JR9530004117
• EVM (Expert Group on Vitamins and Minerals) 2003, Safe Upper Levels for Vitamins and Minerals, UK Food Standards Agency, London, ISBN 1-904026-11-7
• Farandos NM, Yetisen AK, Monteiro MJ, Lowe CR & Yun SH 2014, 'Contact Lens Sensors in Ocular Diagnostics', Advanced Healthcare Materials, doi:10.1002/adhm.201400504, viewed 23 November 2014
• Fehlner TP 1992, 'Introduction', in TP Fehlner (ed.), Inorganometallic chemistry, Plenum, New York, pp. 1–6, ISBN 0-306-43986-7
• Fehlner TP 1990, 'The Metallic Face of Boron,' in AG Sykes (ed.), Advances in Inorganic Chemistry, vol. 35, Academic Press, Orlando, pp. 199–233
• Feng & Jin 2005, Introduction to Condensed Matter Physics: Volume 1, World Scientific, Singapore, ISBN 1-84265-347-4
• Fernelius WC 1982, 'Polonium', Journal of Chemical Education, vol. 59, no. 9, pp. 741–2, doi:10.1021/ed059p741
• Ferro R & Saccone A 2008, Intermetallic Chemistry, Elsevier, Oxford, p. 233, ISBN 0-08-044099-1
• Fesquet AA 1872, A Practical Guide for the Manufacture of Metallic Alloys, trans. A. Guettier, Henry Carey Baird, Philadelphia
• Fine LW & Beall H 1990, Chemistry for Engineers and Scientists, Saunders College Publishing, Philadelphia, ISBN 0-03-021537-4
• Fokwa BPT 2014, 'Borides: Solid-state Chemistry', in Encyclopedia of Inorganic and Bioinorganic Chemistry, John Wiley and Sons, doi:10.1002/9781119951438.eibc0022.pub2
• Foster W 1936, The Romance of Chemistry, D Appleton-Century, New York
• Foster LS & Wrigley AN 1958, 'Periodic Table', in GL Clark, GG Hawley & WA Hamor (eds), The Encyclopedia of Chemistry (Supplement), Reinhold, New York, pp. 215–20
• Friend JN 1953, Man and the Chemical Elements, 1st ed., Charles Scribner's Sons, New York
• Fritz JS & Gjerde DT 2008, Ion Chromatography, John Wiley & Sons, New York, ISBN 3-527-61325-0
• Gary S 2013, 'Poisoned Alloy' the Metal of the Future', News in science, viewed 28 August 2013
• Geckeler S 1987, Optical Fiber Transmission Systems, Artech Hous, Norwood, Massachusetts, ISBN 0-89006-226-9
• German Energy Society 2008, Planning and Installing Photovoltaic Systems: A Guide for Installers, Architects and Engineers, 2nd ed., Earthscan, London, ISBN 978-1-84407-442-6
• Gordh G, Gordh G & Headrick D 2003, A Dictionary of Entomology, CABI Publishing, Wallingford, ISBN 0-85199-655-8
• Gillespie RJ 1998, 'Covalent and Ionic Molecules: Why are BeF2 and AlF3 High Melting Point Solids Whereas BF3 and SiF4 are Gases?', Journal of Chemical Education, vol. 75, no. 7, pp. 923–5, doi:10.1021/ed075p923
• Gillespie RJ & Robinson EA 1963, 'The Sulphuric Acid Solvent System. Part IV. Sulphato Compounds of Arsenic (III)', Canadian Journal of Chemistry, vol. 41, no. 2, pp. 450–458
• Gillespie RJ & Passmore J 1972, 'Polyatomic Cations', Chemistry in Britain, vol. 8, pp. 475–479
• Gladyshev VP & Kovaleva SV 1998, 'Liquidus Shape of the Mercury–Gallium System', Russian Journal of Inorganic Chemistry, vol. 43, no. 9, pp. 1445–6
• Glazov VM, Chizhevskaya SN & Glagoleva NN 1969, Liquid Semiconductors, Plenum, New York
• Glinka N 1965, General Chemistry, trans. D Sobolev, Gordon & Breach, New York
• Glockling F 1969, The Chemistry of Germanium, Academic, London
• Glorieux B, Saboungi ML & Enderby JE 2001, 'Electronic Conduction in Liquid Boron', Europhysics Letters (EPL), vol. 56, no. 1, pp. 81–5, doi:10.1209/epl/i2001-00490-0
• Goldsmith RH 1982, 'Metalloids', Journal of Chemical Education, vol. 59, no. 6, pp. 526–7, doi:10.1021/ed059p526
• Good JM, Gregory O & Bosworth N 1813, 'Arsenicum', in Pantologia: A New Cyclopedia ... of Essays, Treatises, and Systems ... with a General Dictionary of Arts, Sciences, and Words ... , Kearsely, London
• Goodrich BG 1844, A Glance at the Physical Sciences, Bradbury, Soden & Co., Boston
• Gray T 2009, The Elements: A Visual Exploration of Every Known Atom in the Universe, Black Dog & Leventhal, New York, ISBN 978-1-57912-814-2
• Gray T 2010, 'Metalloids (7)', viewed 8 February 2013
• Gray T, Whitby M & Mann N 2011, Mohs Hardness of the Elements, viewed 12 Feb 2012
• Greaves GN, Knights JC & Davis EA 1974, 'Electronic Properties of Amorphous Arsenic', in J Stuke & W Brenig (eds), Amorphous and Liquid Semiconductors: Proceedings, vol. 1, Taylor & Francis, London, pp. 369–74, ISBN 978-0-470-83485-5
• Greenwood NN 2001, 'Main Group Element Chemistry at the Millennium', Journal of the Chemical Society, Dalton Transactions, issue 14, pp. 2055–66, doi:10.1039/b103917m
• Greenwood NN & Earnshaw A 2002, Chemistry of the Elements, 2nd ed., Butterworth-Heinemann, ISBN 0-7506-3365-4
• Guan PF, Fujita T, Hirata A, Liu YH & Chen MW 2012, 'Structural Origins of the Excellent Glass-forming Ability of Pd₄₀Ni₄₀P₂₀', Physical Review Letters, vol. 108, no. 17, pp. 175501–1–5, doi:10.1103/PhysRevLett.108.175501
• Gunn G (ed.) 2014, Critical Metals Handbook,John Wiley & Sons, Chichester, West Sussex, ISBN 9780470671719
• Gupta VB, Mukherjee AK & Cameotra SS 1997, 'Poly(ethylene Terephthalate) Fibres', in MN Gupta & VK Kothari (eds), Manufactured Fibre Technology, Springer Science+Business Media, Dordrecht, pp. 271–317, ISBN 9789401064736
• Haaland A, Helgaker TU, Ruud K & Shorokhov DJ 2000, 'Should Gaseous BF3 and SiF4 be Described as Ionic Compounds?', Journal of Chemical Education, vol. 77, no.8, pp. 1076–80, doi:10.1021/ed077p1076
• Hager T 2006, The Demon under the Microscope, Three Rivers Press, New York, ISBN 978-1-4000-8214-8
• Hai H, Jun H, Yong-Mei L, He-Yong H, Yong C & Kang-Nian F 2012, 'Graphite Oxide as an Efficient and Durable Metal-free Catalyst for Aerobic Oxidative Coupling of Amines to Imines', Green Chemistry, vol. 14, pp. 930–934, doi:10.1039/C2GC16681J
• Haiduc I & Zuckerman JJ 1985, Basic Organometallic Chemistry, Walter de Gruyter, Berlin, ISBN 0-89925-006-8
• Haissinsky M & Coche A 1949, 'New Experiments on the Cathodic Deposition of Radio-elements', Journal of the Chemical Society, pp. S397–400
• Manson SS & Halford GR 2006, Fatigue and Durability of Structural Materials, ASM International, Materials Park, OH, ISBN 0-87170-825-6
• Haller EE 2006, 'Germanium: From its Discovery to SiGe Devices', Materials Science in Semiconductor Processing, vol. 9, nos 4–5, doi:10.1016/j.mssp.2006.08.063, viewed 8 February 2013
• Hamm DI 1969, Fundamental Concepts of Chemistry, Meredith Corporation, New York, ISBN 0-390-40651-1
• Hampel CA & Hawley GG 1966, The Encyclopedia of Chemistry, 3rd ed., Van Nostrand Reinhold, New York
• Hampel CA (ed.) 1968, The Encyclopedia of the Chemical Elements, Reinhold, New York
• Hampel CA & Hawley GG 1976, Glossary of Chemical Terms, Van Nostrand Reinhold, New York, ISBN 0-442-23238-1
• Harding C, Johnson DA & Janes R 2002, Elements of the p Block, Royal Society of Chemistry, Cambridge, ISBN 0-85404-690-9
• Hasan H 2009, The Boron Elements: Boron, Aluminum, Gallium, Indium, Thallium, The Rosen Publishing Group, New York, ISBN 1-4358-5333-4
• Hatcher WH 1949, An Introduction to Chemical Science, John Wiley & Sons, New York
• Hawkes SJ 1999, 'Polonium and Astatine are not Semimetals', Chem 13 News, February, p. 14, ISSN 0703-1157
• Hawkes SJ 2001, 'Semimetallicity', Journal of Chemical Education, vol. 78, no. 12, pp. 1686–7, doi:10.1021/ed078p1686
• Hawkes SJ 2010, 'Polonium and Astatine are not Semimetals', Journal of Chemical Education, vol. 87, no. 8, p. 783, doi:10.1021ed100308w
• Haynes WM (ed.) 2012, CRC Handbook of Chemistry and Physics, 93rd ed., CRC Press, Boca Raton, Florida, ISBN 1-4398-8049-2
• He M, Kravchyk K, Walter M & Kovalenko MV 2014, 'Monodisperse Antimony Nanocrystals for High-Rate Li-ion and Na-ion Battery Anodes: Nano versus Bulk', Nano Letters, vol. 14, no. 3, pp. 1255–1262, doi:10.1021/nl404165c
• Henderson M 2000, Main Group Chemistry, The Royal Society of Chemistry, Cambridge, ISBN 0-85404-617-8
• Hermann A, Hoffmann R & Ashcroft NW 2013, 'Condensed Astatine: Monatomic and Metallic', Physical Review Letters, vol. 111, pp. 11604–1−11604-5, doi:10.1103/PhysRevLett.111.116404
• Hérold A 2006, 'An Arrangement of the Chemical Elements in Several Classes Inside the Periodic Table According to their Common Properties', Comptes Rendus Chimie, vol. 9, no. 1, pp. 148–53, doi:10.1016/j.crci.2005.10.002
• Herzfeld K 1927, 'On Atomic Properties Which Make an Element a Metal', Physical Review, vol. 29, no. 5, pp. 701–705, doi:10.1103PhysRev.29.701
• Hill G & Holman J 2000, Chemistry in Context, 5th ed., Nelson Thornes, Cheltenham, ISBN 0-17-448307-4
• Hiller LA & Herber RH 1960, Principles of Chemistry, McGraw-Hill, New York
• Hindman JC 1968, 'Neptunium', in CA Hampel (ed.), The Encyclopedia of the Chemical Elements, Reinhold, New York, pp. 432–7
• Hoddeson L 2007, 'In the Wake of Thomas Kuhn's Theory of Scientific Revolutions: The Perspective of an Historian of Science,' in S Vosniadou, A Baltas & X Vamvakoussi (eds), Reframing the Conceptual Change Approach in Learning and Instruction, Elsevier, Amsterdam, pp. 25–34, ISBN 978-0-08-045355-2
• Holderness A & Berry M 1979, Advanced Level Inorganic Chemistry, 3rd ed., Heinemann Educational Books, London, ISBN 0-435-65435-7
• Holt, Rinehart & Wilson c. 2007 'Why Polonium and Astatine are not Metalloids in HRW texts', viewed 8 February 2013
• Hopkins BS & Bailar JC 1956, General Chemistry for Colleges, 5th ed., D. C. Heath, Boston
• Horvath 1973, 'Critical Temperature of Elements and the Periodic System', Journal of Chemical Education, vol. 50, no. 5, pp. 335–6, doi:10.1021/ed050p335
• Hosseini P, Wright CD & Bhaskaran H 2014, 'An optoelectronic framework enabled by low-dimensional phase-change films,' Nature, vol. 511, pp. 206–211, doi:10.1038/nature13487
• Houghton RP 1979, Metal Complexes in Organic Chemistry, Cambridge University Press, Cambridge, ISBN 0-521-21992-2
• House JE 2008, Inorganic Chemistry, Academic Press (Elsevier), Burlington, Massachusetts, ISBN 0-12-356786-6
• House JE & House KA 2010, Descriptive Inorganic Chemistry, 2nd ed., Academic Press, Burlington, Massachusetts, ISBN 0-12-088755-X
• Housecroft CE & Sharpe AG 2008, Inorganic Chemistry, 3rd ed., Pearson Education, Harlow, ISBN 978-0-13-175553-6
• Hultgren HH 1966, 'Metalloids', in GL Clark & GG Hawley (eds), The Encyclopedia of Inorganic Chemistry, 2nd ed., Reinhold Publishing, New York
• Hunt A 2000, The Complete A-Z Chemistry Handbook, 2nd ed., Hodder & Stoughton, London, ISBN 0-340-77218-2
• Inagaki M 2000, New Carbons: Control of Structure and Functions, Elsevier, Oxford, ISBN 0-08-043713-3
• IUPAC 1959, Nomenclature of Inorganic Chemistry, 1st ed., Butterworths, London
• IUPAC 1971, Nomenclature of Inorganic Chemistry, 2nd ed., Butterworths, London, ISBN 0-408-70168-4
• IUPAC 2005, Nomenclature of Inorganic Chemistry (the "Red Book"), NG Connelly & T Damhus eds, RSC Publishing, Cambridge, ISBN 0-85404-438-8
• IUPAC 2006–, Compendium of Chemical Terminology (the "Gold Book"), 2nd ed., by M Nic, J Jirat & B Kosata, with updates compiled by A Jenkins, ISBN 0-9678550-9-8, doi:10.1351/goldbook
• James M, Stokes R, Ng W & Moloney J 2000, Chemical Connections 2: VCE Chemistry Units 3 & 4, John Wiley & Sons, Milton, Queensland, ISBN 0-7016-3438-3
• Jaouen G & Gibaud S 2010, 'Arsenic-based Drugs: From Fowler's solution to Modern Anticancer Chemotherapy', Medicinal Organometallic Chemistry, vol. 32, pp. 1–20, doi:10.1007/978-3-642-13185-1_1
• Jaskula BW 2013, Mineral Commodity Profiles: Gallium, US Geological Survey
• Jenkins GM & Kawamura K 1976, Polymeric Carbons—Carbon Fibre, Glass and Char, Cambridge University Press, Cambridge, ISBN 0-521-20693-6
• Jezequel G & Thomas J 1997, 'Experimental Band Structure of Semimetal Bismuth', Physical Review B, vol. 56, no. 11, pp. 6620–6, doi:10.1103/PhysRevB.56.6620
• Johansen G & Mackintosh AR 1970, 'Electronic Structure and Phase Transitions in Ytterbium', Solid State Communications, vol. 8, no. 2, pp. 121–4
• Jolly WL & Latimer WM 1951, 'The Heat of Oxidation of Germanous Iodide and the Germanium Oxidation Potentials', University of California Radiation Laboratory, Berkeley
• Jolly WL 1966, The Chemistry of the Non-metals, Prentice-Hall, Englewood Cliffs, New Jersey
• Jones BW 2010, Pluto: Sentinel of the Outer Solar System, Cambridge University, Cambridge, ISBN 978-0-521-19436-5
• Kaminow IP & Li T 2002 (eds), Optical Fiber Telecommunications, Volume IVA, Academic Press, San Diego, ISBN 0-12-395172-0
• Karabulut M, Melnik E, Stefan R, Marasinghe GK, Ray CS, Kurkjian CR & Day DE 2001, 'Mechanical and Structural Properties of Phosphate Glasses', Journal of Non-Crystalline Solids, vol. 288, nos. 1–3, pp. 8–17, doi:10.1016/S0022-3093(01)00615-9
• Kauthale SS, Tekali SU, Rode AB, Shinde SV, Ameta KL & Pawar RP 2015, 'Silica Sulfuric Acid: A Simple and Powerful Heterogenous Catalyst in Organic Synthesis', in KL Ameta & A Penoni, Heterogeneous Catalysis: A Versatile Tool for the Synthesis of Bioactive Heterocycles, CRC Press, Boca Raton, Florida, pp. 133–162, ISBN 9781466594821
• Kaye GWC & Laby TH 1973, Tables of Physical and Chemical Constants, 14th ed., Longman, London, ISBN 0-582-46326-2
• Keall JHH, Martin NH & Tunbridge RE 1946, 'A Report of Three Cases of Accidental Poisoning by Sodium Tellurite', British Journal of Industrial Medicine, vol. 3, no. 3, pp. 175–6
• Keevil D 1989, 'Aluminium', in MN Patten (ed.), Information Sources in Metallic Materials, Bowker–Saur, London, pp. 103–119, ISBN 0-408-01491-1
• Keller C 1985, 'Preface', in Kugler & Keller
• Kelter P, Mosher M & Scott A 2009, Chemistry: the Practical Science, Houghton Mifflin, Boston, ISBN 0-547-05393-2
• Kennedy T, Mullane E, Geaney H, Osiak M, O'Dwyer C & Ryan KM 2014, 'High-Performance Germanium Nanowire-Based Lithium-Ion Battery Anodes Extending over 1000 Cycles Through in Situ Formation of a Continuous Porous Network', Nano-letters, vol. 14, no. 2, pp. 716–723, doi:10.1021/nl403979s
• Kent W 1950, Kent's Mechanical Engineers' Handbook, 12th ed., vol. 1, John Wiley & Sons, New York
• King EL 1979, Chemistry, Painter Hopkins, Sausalito, California, ISBN 0-05-250726-2
• King RB 1994, 'Antimony: Inorganic Chemistry', in RB King (ed), Encyclopedia of Inorganic Chemistry, John Wiley, Chichester, pp. 170–5, ISBN 0-471-93620-0
• King RB 2004, 'The Metallurgist's Periodic Table and the Zintl-Klemm Concept', in DH Rouvray & RB King (eds), The Periodic Table: Into the 21st Century, Research Studies Press, Baldock, Hertfordshire, pp. 191–206, ISBN 0-86380-292-3
• Kinjo R, Donnadieu B, Celik MA, Frenking G & Bertrand G 2011, 'Synthesis and Characterization of a Neutral Tricoordinate Organoboron Isoelectronic with Amines', Science, pp. 610–613, doi:10.1126/science.1207573
• Kitaĭgorodskiĭ AI 1961, Organic Chemical Crystallography, Consultants Bureau, New York
• Kleinberg J, Argersinger WJ & Griswold E 1960, Inorganic Chemistry, DC Health, Boston
• Klement W, Willens RH & Duwez P 1960, 'Non-Crystalline Structure in Solidified Gold–Silicon Alloys', Nature, vol. 187, pp. 869–70, doi|10.1038/187869b0
• Klemm W 1950, 'Einige Probleme aus der Physik und der Chemie der Halbmetalle und der Metametalle', Angewandte Chemie, vol. 62, no. 6, pp. 133–42
• Klug HP & Brasted RC 1958, Comprehensive Inorganic Chemistry: The Elements and Compounds of Group IV A, Van Nostrand, New York
• Kneen WR, Rogers MJW & Simpson P 1972, Chemistry: Facts, Patterns, and Principles, Addison-Wesley, London, ISBN 0-201-03779-3
• Kohl AL & Nielsen R 1997, Gas Purification, 5th ed., Gulf Valley Publishing, Houston, Texas, ISBN 0884152200
• Kolobov AV & Tominaga J 2012, Chalcogenides: Metastability and Phase Change Phenomena, Springer-Verlag, Heidelberg, ISBN 978-3-642-28705-3
• Kolthoff IM & Elving PJ 1978, Treatise on Analytical Chemistry. Analytical Chemistry of Inorganic and Organic Compounds: Antimony, Arsenic, Boron, Carbon, Molybenum, Tungsten, Wiley Interscience, New York, ISBN 0-471-49998-6
• Kondrat'ev SN & Mel'nikova SI 1978, 'Preparation and Various Characteristics of Boron Hydrogen Sulfates', Russian Journal of Inorganic Chemistry, vol. 23, no. 6, pp. 805–807
• Kopp JG, Lipták BG & Eren H 000, 'Magnetic Flowmeters', in BG Lipták (ed.), Instrument Engineers' Handbook, 4th ed., vol. 1, Process Measurement and Analysis, CRC Press, Boca Raton, Florida, pp. 208–224, ISBN 0-8493-1083-0
• Korenman IM 1959, 'Regularities in Properties of Thallium', Journal of General Chemistry of the USSR, English translation, Consultants Bureau, New York, vol. 29, no. 2, pp. 1366–90, ISSN 0022-1279
• Kosanke KL, Kosanke BJ & Dujay RC 2002, 'Pyrotechnic Particle Morphologies—Metal Fuels', in Selected Pyrotechnic Publications of K.L. and B.J. Kosanke Part 5 (1998 through 2000), Journal of Pyrotechnics, Whitewater, CO, ISBN 1-889526-13-4
• Kotz JC, Treichel P & Weaver GC 2009, Chemistry and Chemical Reactivity, 7th ed., Brooks/Cole, Belmont, California, ISBN 1-4390-4131-8
• Kozyrev PT 1959, 'Deoxidized Selenium and the Dependence of its Electrical Conductivity on Pressure. II', Physics of the Solid State, translation of the journal Solid State Physics (Fizika tverdogo tela) of the Academy of Sciences of the USSR, vol. 1, pp. 102–10
• Kraig RE, Roundy D & Cohen ML 2004, 'A Study of the Mechanical and Structural Properties of Polonium', Solid State Communications, vol. 129, issue 6, Feb, pp. 411–13, doi:10.1016/j.ssc.2003.08.001
• Krannich LK & Watkins CL 2006, 'Arsenic: Organoarsenic chemistry,' Encyclopedia of inorganic chemistry, viewed 12 Feb 2012
• Kreith F & Goswami DY (eds) 2005, The CRC Handbook of Mechanical Engineering, 2nd ed., Boca Raton, Florida, ISBN 0-8493-0866-6
• Krishnan S, Ansell S, Felten J, Volin K & Price D 1998, 'Structure of Liquid Boron', Physical Review Letters, vol. 81, no. 3, pp. 586–9, doi:10.1103/PhysRevLett.81.586
• Kross B 2011, 'What's the melting point of steel?', Questions and Answers, Thomas Jefferson National Accelerator Facility, Newport News, VA
• Kudryavtsev AA 1974, The Chemistry & Technology of Selenium and Tellurium, translated from the 2nd Russian edition and revised by EM Elkin, Collet's, London, ISBN 0-569-08009-6
• Kugler HK & Keller C (eds) 1985, Gmelin Handbook of Inorganic and Organometallic chemistry, 8th ed., 'At, Astatine', system no. 8a, Springer-Verlag, Berlin, ISBN 3-540-93516-9
• Ladd M 1999, Crystal Structures: Lattices and Solids in Stereoview, Horwood Publishing, Chichester, ISBN 1-898563-63-2
• Le Bras M, Wilkie CA & Bourbigot S (eds) 2005, Fire Retardancy of Polymers: New Applications of Mineral Fillers, Royal Society of Chemistry, Cambridge, ISBN 0-85404-582-1
• Lee J, Lee EK, Joo W, Jang Y, Kim B, Lim JY, Choi S, Ahn SJ, Ahn JR, Park M, Yang C, Choi BL, Hwang S & Whang D 2014, 'Wafer-Scale Growth of Single-Crystal Monolayer Graphene on Reusable Hydrogen-Terminated Germanium', Science, vol. 344, no. 6181, pp. 286–289, doi:10.1126/science.1252268
• Legit D, Friák M & Šob M 2010, 'Phase Stability, Elasticity, and Theoretical Strength of Polonium from First Principles,' Physical Review B, vol. 81, pp. 214118–1–19, doi:10.1103/PhysRevB.81.214118
• Lehto Y & Hou X 2011, Chemistry and Analysis of Radionuclides: Laboratory Techniques and Methodology, Wiley-VCH, Weinheim, ISBN 978-3-527-32658-7
• Lewis RJ 1993, Hawley's Condensed Chemical Dictionary, 12th ed., Van Nostrand Reinhold, New York, ISBN 0-442-01131-8
• Li XP 1990, 'Properties of Liquid Arsenic: A Theoretical Study', Physical Review B, vol. 41, no. 12, pp. 8392–406, doi:10.1103/PhysRevB.41.8392
• Lide DR (ed.) 2005, 'Section 14, Geophysics, Astronomy, and Acoustics; Abundance of Elements in the Earth's Crust and in the Sea', in CRC Handbook of Chemistry and Physics, 85th ed., CRC Press, Boca Raton, FL, pp. 14–17, ISBN 0-8493-0485-7
• Lidin RA 1996, Inorganic Substances Handbook, Begell House, New York, ISBN 1-56700-065-7
• Lindsjö M, Fischer A & Kloo L 2004, 'Sb8(GaCl4)2: Isolation of a Homopolyatomic Antimony Cation', Angewandte Chemie, vol. 116, no. 19, pp. 2594–2597, doi:10.1002/ange.200353578
• Lipscomb CA 1972 Pyrotechnics in the '70's A Materials Approach, Naval Ammunition Depot, Research and Development Department, Crane, IN
• Lister MW 1965, Oxyacids, Oldbourne Press, London
• Liu ZK, Jiang J, Zhou B, Wang ZJ, Zhang Y, Weng HM, Prabhakaran D, Mo S-K, Peng H, Dudin P, Kim T, Hoesch M, Fang Z, Dai X, Shen ZX, Feng DL, Hussain Z & Chen YL 2014, 'A Stable Three-dimensional Topological Dirac Semimetal Cd₃As₂', Nature Materials, vol. 13, pp. 677–681, doi:10.1038/nmat3990
• Locke EG, Baechler RH, Beglinger E, Bruce HD, Drow JT, Johnson KG, Laughnan DG, Paul BH, Rietz RC, Saeman JF & Tarkow H 1956, 'Wood', in RE Kirk & DF Othmer (eds), Encyclopedia of Chemical Technology, vol. 15, The Interscience Encyclopedia, New York, pp. 72–102
• Löffler JF, Kündig AA & Dalla Torre FH 2007, 'Rapid Solidification and Bulk Metallic Glasses—Processing and Properties,' in JR Groza, JF Shackelford, EJ Lavernia EJ & MT Powers (eds), Materials Processing Handbook, CRC Press, Boca Raton, Florida, pp. 17–1–44, ISBN 0-8493-3216-8
• Long GG & Hentz FC 1986, Problem Exercises for General Chemistry, 3rd ed., John Wiley & Sons, New York, ISBN 0-471-82840-8
• Lovett DR 1977, Semimetals & Narrow-Bandgap Semi-conductors, Pion, London, ISBN 0-85086-060-1
• Lutz J, Schlangenotto H, Scheuermann U, De Doncker R 2011, Semiconductor Power Devices: Physics, Characteristics, Reliability, Springer-Verlag, Berlin, ISBN 3-642-11124-6
• Masters GM & Ela W 2008, Introduction to Environmental Engineering and Science, 3rd ed., Prentice Hall, Upper Saddle River, New Jersey, ISBN 978-0-13-148193-0
• MacKay KM, MacKay RA & Henderson W 2002, Introduction to Modern Inorganic Chemistry, 6th ed., Nelson Thornes, Cheltenham, ISBN 0-7487-6420-8
• MacKenzie D, 2015 'Gas! Gas! Gas!', New Scientist, vol. 228, no. 3044, pp. 34–37
• Madelung O 2004, Semiconductors: Data Handbook, 3rd ed., Springer-Verlag, Berlin, ISBN 978-3-540-40488-0
• Maeder T 2013, 'Review of Bi₂O₃ Based Glasses for Electronics and Related Applications, International Materials Reviews, vol. 58, no. 1, pp. 3‒40, doi:10.1179/1743280412Y.0000000010
• Mahan BH 1965, University Chemistry, Addison-Wesley, Reading, Massachusetts
• Mainiero C,2014, 'Picatinny chemist wins Young Scientist Award for work on smoke grenades', U.S. Army, Picatinny Public Affairs, 2 April, viewed 9 June 2017
• Manahan SE 2001, Fundamentals of Environmental Chemistry, 2nd ed., CRC Press, Boca Raton, Florida, ISBN 1-56670-491-X
• Mann JB, Meek TL & Allen LC 2000, 'Configuration Energies of the Main Group Elements', Journal of the American Chemical Society, vol. 122, no. 12, pp. 2780–3, doi:10.1021ja992866e
• Marezio M & Licci F 2000, 'Strategies for Tailoring New Superconducting Systems', in X Obradors, F Sandiumenge & J Fontcuberta (eds), Applied Superconductivity 1999: Large scale applications, volume 1 of Applied Superconductivity 1999: Proceedings of EUCAS 1999, the Fourth European Conference on Applied Superconductivity, held in Sitges, Spain, 14–17 September 1999, Institute of Physics, Bristol, pp. 11–16, ISBN 0-7503-0745-5
• Marković N, Christiansen C & Goldman AM 1998, 'Thickness-Magnetic Field Phase Diagram at the Superconductor-Insulator Transition in 2D', Physical Review Letters, vol. 81, no. 23, pp. 5217–20, doi:10.1103/PhysRevLett.81.5217
• Massey AG 2000, Main Group Chemistry, 2nd ed., John Wiley & Sons, Chichester, ISBN 0-471-49039-3
• Masterton WL & Slowinski EJ 1977, Chemical Principles, 4th ed., W. B. Saunders, Philadelphia, ISBN 0-7216-6173-4
• Matula RA 1979, 'Electrical Resistivity of Copper, Gold, Palladium, and Silver,' Journal of Physical and Chemical Reference Data, vol. 8, no. 4, pp. 1147–298, doi:10.1063/1.555614
• McKee DW 1984, 'Tellurium—An Unusual Carbon Oxidation Catalyst', Carbon, vol. 22, no. 6, doi:10.1016/0008-6223(84)90084-8, pp. 513–516
• McMurray J & Fay RC 2009, General Chemistry: Atoms First, Prentice Hall, Upper Saddle River, New Jersey, ISBN 0-321-57163-0
• McQuarrie DA & Rock PA 1987, General Chemistry, 3rd ed., WH Freeman, New York, ISBN 0-7167-2169-4
• Mellor JW 1964, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 9, John Wiley, New York
• Mellor JW 1964a, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 11, John Wiley, New York
• Mendeléeff DI 1897, The Principles of Chemistry, vol. 2, 5th ed., trans. G Kamensky, AJ Greenaway (ed.), Longmans, Green & Co., London
• Meskers CEM, Hagelüken C & Van Damme G 2009, 'Green Recycling of EEE: Special and Precious Metal EEE', in SM Howard, P Anyalebechi & L Zhang (eds), Proceedings of Sessions and Symposia Sponsored by the Extraction and Processing Division (EPD) of The Minerals, Metals and Materials Society (TMS), held during the TMS 2009 Annual Meeting & Exhibition San Francisco, California, February 15–19, 2009, The Minerals, Metals and Materials Society, Warrendale, Pennsylvania, ISBN 978-0-87339-732-2, pp. 1131–6
• Metcalfe HC, Williams JE & Castka JF 1974, Modern Chemistry, Holt, Rinehart and Winston, New York, ISBN 0-03-089450-6
• Meyer JS, Adams WJ, Brix KV, Luoma SM, Mount DR, Stubblefield WA & Wood CM (eds) 2005, Toxicity of Dietborne Metals to Aquatic Organisms, Proceedings from the Pellston Workshop on Toxicity of Dietborne Metals to Aquatic Organisms, 27 July–1 August 2002, Fairmont Hot Springs, British Columbia, Canada, Society of Environmental Toxicology and Chemistry, Pensacola, Florida, ISBN 1-880611-70-8
• Mhiaoui S, Sar F, Gasser J 2003, 'Influence of the History of a Melt on the Electrical Resistivity of Cadmium–Antimony Liquid Alloys', Intermetallics, vol. 11, nos 11–12, pp. 1377–82, doi:10.1016/j.intermet.2003.09.008
• Miller GJ, Lee C & Choe W 2002, 'Structure and Bonding Around the Zintl border', in G Meyer, D Naumann & L Wesermann (eds), Inorganic chemistry highlights, Wiley-VCH, Weinheim, pp. 21–53, ISBN 3-527-30265-4
• Millot F, Rifflet JC, Sarou-Kanian V & Wille G 2002, 'High-Temperature Properties of Liquid Boron from Contactless Techniques', International Journal of Thermophysics, vol. 23, no. 5, pp. 1185–95, doi:10.1023/A:1019836102776
• Mingos DMP 1998, Essential Trends in Inorganic Chemistry, Oxford University, Oxford, ISBN 0-19-850108-0
• Moeller T 1954, Inorganic Chemistry: An Advanced Textbook, John Wiley & Sons, New York
• Mokhatab S & Poe WA 2012, Handbook of Natural Gas Transmission and Processing, 2nd ed., Elsevier, Kidlington, Oxford, ISBN 9780123869142
• Molina-Quiroz RC, Muñoz-Villagrán CM, de la Torre E, Tantaleán JC, Vásquez CC & Pérez-Donoso JM 2012, 'Enhancing the Antibiotic Antibacterial Effect by Sub Lethal Tellurite Concentrations: Tellurite and Cefotaxime Act Synergistically in Escherichia Coli', PloS (Public Library of Science) ONE, vol. 7, no. 4, doi:10.1371/journal.pone.0035452
• Monconduit L, Evain M, Boucher F, Brec R & Rouxel J 1992, 'Short Te ... Te Bonding Contacts in a New Layered Ternary Telluride: Synthesis and crystal structure of 2D Nb₃Ge_xTe₆ (x ≃ 0.9)', Zeitschrift für Anorganische und Allgemeine Chemie, vol. 616, no. 10, pp. 177–182, doi:10.1002/zaac.19926161028
• Moody B 1991, Comparative Inorganic Chemistry, 3rd ed., Edward Arnold, London, ISBN 0-7131-3679-0
• Moore LJ, Fassett JD, Travis JC, Lucatorto TB & Clark CW 1985, 'Resonance-Ionization Mass Spectrometry of Carbon', Journal of the Optical Society of America B, vol. 2, no. 9, pp. 1561–5, doi:10.1364/JOSAB.2.001561
• Moore JE 2010, 'The Birth of Topological Insulators,' Nature, vol. 464, pp. 194–198, doi:10.1038/nature08916
• Moore JE 2011, Topological insulators, IEEE Spectrum, viewed 15 December 2014
• Moore JT 2011, Chemistry for Dummies, 2nd ed., John Wiley & Sons, New York, ISBN 1-118-09292-9
• Moore NC 2014, '45-year Physics Mystery Shows a Path to Quantum Transistors', Michigan News, viewed 17 December 2014
• Morgan WC 1906, Qualitative Analysis as a Laboratory Basis for the Study of General Inorganic Chemistry, The Macmillan Company, New York
• Morita A 1986, 'Semiconducting Black Phosphorus', Journal of Applied Physics A, vol. 39, no. 4, pp. 227–42, doi:10.1007/BF00617267
• Moss TS 1952, Photoconductivity in the Elements, London, Butterworths
• Muncke J 2013, 'Antimony Migration from PET: New Study Investigates Extent of Antimony Migration from Polyethylene Terephthalate (PET) Using EU Migration Testing Rules', Food Packaging Forum, April 2
• Murray JF 1928, 'Cable-Sheath Corrosion', Electrical World, vol. 92, Dec 29, pp. 1295–7, ISSN 0013-4457
• Nagao T, Sadowski1 JT, Saito M, Yaginuma S, Fujikawa Y, Kogure T, Ohno T, Hasegawa Y, Hasegawa S & Sakurai T 2004, 'Nanofilm Allotrope and Phase Transformation of Ultrathin Bi Film on Si(111)-7×7', Physical Review Letters, vol. 93, no. 10, pp. 105501–1–4, doi:10.1103/PhysRevLett.93.105501
• Neuburger MC 1936, 'Gitterkonstanten für das Jahr 1936' (in German), Zeitschrift für Kristallographie, vol. 93, pp. 1–36, ISSN 0044-2968
• Nickless G 1968, Inorganic Sulphur Chemistry, Elsevier, Amsterdam
• Nielsen FH 1998, 'Ultratrace Elements in Nutrition: Current Knowledge and Speculation', The Journal of Trace Elements in Experimental Medicine, vol. 11, pp. 251–74, doi:10.1002/(SICI)1520-670X(1998)11:2/3<251::AID-JTRA15>3.0.CO;2-Q
• NIST (National Institute of Standards and Technology) 2010, Ground Levels and Ionization Energies for Neutral Atoms, by WC Martin, A Musgrove, S Kotochigova & JE Sansonetti, viewed 8 February 2013
• National Research Council 1984, The Competitive Status of the U.S. Electronics Industry: A Study of the Influences of Technology in Determining International Industrial Competitive Advantage, National Academy Press, Washington, DC, ISBN 0-309-03397-7
• New Scientist 1975, 'Chemistry on the Islands of Stability', 11 Sep, p. 574, ISSN 1032-1233
• New Scientist 2014, 'Colour-changing metal to yield thin, flexible displays', vol. 223, no. 2977
• Oderberg DS 2007, Real Essentialism, Routledge, New York, ISBN 1-134-34885-1
• Oxford English Dictionary 1989, 2nd ed., Oxford University, Oxford, ISBN 0-19-861213-3
• Oganov AR, Chen J, Gatti C, Ma Y, Ma Y, Glass CW, Liu Z, Yu T, Kurakevych OO & Solozhenko VL 2009, 'Ionic High-Pressure Form of Elemental Boron', Nature, vol. 457, 12 Feb, pp. 863–8, doi:10.1038/nature07736
• Oganov AR 2010, 'Boron Under Pressure: Phase Diagram and Novel High Pressure Phase,' in N Ortovoskaya N & L Mykola L (eds), Boron Rich Solids: Sensors, Ultra High Temperature Ceramics, Thermoelectrics, Armor, Springer, Dordrecht, pp. 207–25, ISBN 90-481-9823-2
• Ogata S, Li J & Yip S 2002, 'Ideal Pure Shear Strength of Aluminium and Copper', Science, vol. 298, no. 5594, 25 October, pp. 807–10, doi:10.1126/science.1076652
• O'Hare D 1997, 'Inorganic intercalation compounds' in DW Bruce & D O'Hare (eds), Inorganic materials, 2nd ed., John Wiley & Sons, Chichester, pp. 171–254, ISBN 0-471-96036-5
• Okajima Y & Shomoji M 1972, Viscosity of Dilute Amalgams', Transactions of the Japan Institute of Metals, vol. 13, no. 4, pp. 255–8, ISSN 0021-4434
• Oldfield JE, Allaway WH, HA Laitinen, HW Lakin & OH Muth 1974, 'Tellurium', in Geochemistry and the Environment, Volume 1: The Relation of Selected Trace Elements to Health and Disease, US National Committee for Geochemistry, Subcommittee on the Geochemical Environment in Relation to Health and Disease, National Academy of Sciences, Washington, ISBN 0-309-02223-1
• Oliwenstein L 2011, 'Caltech-Led Team Creates Damage-Tolerant Metallic Glass', California Institute of Technology, 12 January, viewed 8 February 2013
• Olmsted J & Williams GM 1997, Chemistry, the Molecular Science, 2nd ed., Wm C Brown, Dubuque, Iowa, ISBN 0-8151-8450-6
• Ordnance Office 1863, The Ordnance Manual for the use of the Officers of the Confederate States Army, 1st ed., Evans & Cogswell, Charleston, SC
• Orton JW 2004, The Story of Semiconductors, Oxford University, Oxford, ISBN 0-19-853083-8
• Owen SM & Brooker AT 1991, A Guide to Modern Inorganic Chemistry, Longman Scientific & Technical, Harlow, Essex, ISBN 0-582-06439-2
• Oxtoby DW, Gillis HP & Campion A 2008, Principles of Modern Chemistry, 6th ed., Thomson Brooks/Cole, Belmont, California, ISBN 0-534-49366-1
• Pan K, Fu Y & Huang T 1964, 'Polarographic Behavior of Germanium(II)-Perchlorate in Perchloric Acid Solutions', Journal of the Chinese Chemical Society, pp. 176–184, doi:10.1002/jccs.196400020
• Parise JB, Tan K, Norby P, Ko Y & Cahill C 1996, 'Examples of Hydrothermal Titration and Real Time X-ray Diffraction in the Synthesis of Open Frameworks', MRS Proceedings, vol. 453, pp. 103–14, doi:10.1557/PROC-453-103
• Parish RV 1977, The Metallic Elements, Longman, London, ISBN 0-582-44278-8
• Parkes GD & Mellor JW 1943, Mellor's Nodern Inorganic Chemistry, Longmans, Green and Co., London
• Parry RW, Steiner LE, Tellefsen RL & Dietz PM 1970, Chemistry: Experimental Foundations, Prentice-Hall/Martin Educational, Sydney, ISBN 0-7253-0100-7
• Partington 1944, A Text-book of Inorganic Chemistry, 5th ed., Macmillan, London
• Pashaey BP & Seleznev VV 1973, 'Magnetic Susceptibility of Gallium-Indium Alloys in Liquid State', Russian Physics Journal, vol. 16, no. 4, pp. 565–6, doi:10.1007/BF00890855
• Patel MR 2012, Introduction to Electrical Power and Power Electronics CRC Press, Boca Raton, ISBN 978-1-4665-5660-7
• Paul RC, Puri JK, Sharma RD & Malhotra KC 1971, 'Unusual Cations of Arsenic', Inorganic and Nuclear Chemistry Letters, vol. 7, no. 8, pp. 725–728, doi:10.1016/0020-1650(71)80079-X
• Pauling L 1988, General Chemistry, Dover Publications, New York, ISBN 0-486-65622-5
• Pearson WB 1972, The Crystal Chemistry and Physics of Metals and Alloys, Wiley-Interscience, New York, ISBN 0-471-67540-7
• Perry DL 2011, Handbook of Inorganic Compounds, 2nd ed., CRC Press, Boca Raton, Florida, ISBN 9781439814611
• Peryea FJ 1998, 'Historical Use of Lead Arsenate Insecticides, Resulting Soil Contamination and Implications for Soil Remediation, Proceedings', 16th World Congress of Soil Science, Montpellier, France, 20–26 August
• Phillips CSG & Williams RJP 1965, Inorganic Chemistry, I: Principles and Non-metals, Clarendon Press, Oxford
• Pinkerton J 1800, Petralogy. A Treatise on Rocks, vol. 2, White, Cochrane, and Co., London
• Poojary DM, Borade RB & Clearfield A 1993, 'Structural Characterization of Silicon Orthophosphate', Inorganica Chimica Acta, vol. 208, no. 1, pp. 23–9, doi:10.1016/S0020-1693(00)82879-0
• Pourbaix M 1974, Atlas of Electrochemical Equilibria in Aqueous Solutions, 2nd English edition, National Association of Corrosion Engineers, Houston, ISBN 0-915567-98-9
• Powell HM & Brewer FM 1938, 'The Structure of Germanous Iodide', Journal of the Chemical Society,, pp. 197–198, doi:10.1039/JR9380000197
• Powell P 1988, Principles of Organometallic Chemistry, Chapman and Hall, London, ISBN 0-412-42830-X
• Prakash GKS & Schleyer PvR (eds) 1997, Stable Carbocation Chemistry, John Wiley & Sons, New York, ISBN 0-471-59462-8
• Prudenziati M 1977, IV. 'Characterization of Localized States in β-Rhombohedral Boron', in VI Matkovich (ed.), Boron and Refractory Borides, Springer-Verlag, Berlin, pp. 241–61, ISBN 0-387-08181-X
• Puddephatt RJ & Monaghan PK 1989, The Periodic Table of the Elements, 2nd ed., Oxford University, Oxford, ISBN 0-19-855516-4
• Pyykkö P 2012, 'Relativistic Effects in Chemistry: More Common Than You Thought', Annual Review of Physical Chemistry, vol. 63, pp. 45‒64 (56), doi: 10.1146/annurev-physchem-032511-143755
• Rao CNR & Ganguly P 1986, 'A New Criterion for the Metallicity of Elements', Solid State Communications, vol. 57, no. 1, pp. 5–6, doi:10.1016/0038-1098(86)90659-9
• Rao KY 2002, Structural Chemistry of Glasses, Elsevier, Oxford, ISBN 0-08-043958-6
• Rausch MD 1960, 'Cyclopentadienyl Compounds of Metals and Metalloids', Journal of Chemical Education, vol. 37, no. 11, pp. 568–78, doi:10.1021/ed037p568
• Rayner-Canham G & Overton T 2006, Descriptive Inorganic Chemistry, 4th ed., WH Freeman, New York, ISBN 0-7167-8963-9
• Rayner-Canham G 2011, 'Isodiagonality in the Periodic Table', Foundations of chemistry, vol. 13, no. 2, pp. 121–9, doi:10.1007/s10698-011-9108-y
• Reardon M 2005, 'IBM Doubles Speed of Germanium chips', CNET News, August 4, viewed 27 December 2013
• Regnault MV 1853, Elements of Chemistry, vol. 1, 2nd ed., Clark & Hesser, Philadelphia
• Reilly C 2002, Metal Contamination of Food, Blackwell Science, Oxford, ISBN 0-632-05927-3
• Reilly 2004, The Nutritional Trace Metals, Blackwell, Oxford, ISBN 1-4051-1040-6
• Restrepo G, Mesa H, Llanos EJ & Villaveces JL 2004, 'Topological Study of the Periodic System', Journal of Chemical Information and Modelling, vol. 44, no. 1, pp. 68–75, doi:10.1021/ci034217z
• Restrepo G, Llanos EJ & Mesa H 2006, 'Topological Space of the Chemical Elements and its Properties', Journal of Mathematical Chemistry, vol. 39, no. 2, pp. 401–16, doi: 10.1007/s10910-005-9041-1
• Řezanka T & Sigler K 2008, 'Biologically Active Compounds of Semi-Metals', Studies in Natural Products Chemistry, vol. 35, pp. 585–606, doi:10.1016/S1572-5995(08)80018-X
• Richens DT 1997, The Chemistry of Aqua Ions, John Wiley & Sons, Chichester, ISBN 0-471-97058-1
• Rochow EG 1957, The Chemistry of Organometallic Compounds, John Wiley & Sons, New York
• Rochow EG 1966, The Metalloids, DC Heath and Company, Boston
• Rochow EG 1973, 'Silicon', in JC Bailar, HJ Emeléus, R Nyholm & AF Trotman-Dickenson (eds), Comprehensive Inorganic Chemistry, vol. 1, Pergamon, Oxford, pp. 1323–1467, ISBN 0-08-015655-X
• Rochow EG 1977, Modern Descriptive Chemistry, Saunders, Philadelphia, ISBN 0-7216-7628-6
• Rodgers G 2011, Descriptive Inorganic, Coordination, & Solid-state Chemistry, Brooks/Cole, Belmont, CA, ISBN 0-8400-6846-8
• Roher GS 2001, Structure and Bonding in Crystalline Materials, Cambridge University Press, Cambridge, ISBN 0-521-66379-2
• Rossler K 1985, 'Handling of Astatine', pp. 140–56, in Kugler & Keller
• Rothenberg GB 1976, Glass Technology, Recent Developments, Noyes Data Corporation, Park Ridge, New Jersey, ISBN 0-8155-0609-0
• Roza G 2009, Bromine, Rosen Publishing, New York, ISBN 1-4358-5068-8
• Rupar PA, Staroverov VN & Baines KM 2008, 'A Cryptand-Encapsulated Germanium(II) Dication', Science, vol. 322, no. 5906, pp. 1360–1363, doi:10.1126/science.1163033
• Russell AM & Lee KL 2005, Structure-Property Relations in Nonferrous Metals, Wiley-Interscience, New York, ISBN 0-471-64952-X
• Russell MS 2009, The Chemistry of Fireworks, 2nd ed., Royal Society of Chemistry, ISBN 978-0-85404-127-5
• Sacks MD 1998, 'Mullitization Behavior of Alpha Alumina Silica Microcomposite Powders', in AP Tomsia & AM Glaeser (eds), Ceramic Microstructures: Control at the Atomic Level, proceedings of the International Materials Symposium on Ceramic Microstructures '96: Control at the Atomic Level, June 24–27, 1996, Berkeley, CA, Plenum Press, New York, pp. 285–302, ISBN 0-306-45817-9
• Salentine CG 1987, 'Synthesis, Characterization, and Crystal Structure of a New Potassium Borate, KB₃O₅•3H₂O', Inorganic Chemistry, vol. 26, no. 1, pp. 128–32, doi:10.1021/ic00248a025
• Samsonov GV 1968, Handbook of the Physiochemical Properties of the Elements, I F I/Plenum, New York
• Savvatimskiy AI 2005, 'Measurements of the Melting Point of Graphite and the Properties of Liquid Carbon (a review for 1963–2003)', Carbon, vol. 43, no. 6, pp. 1115–42, doi:10.1016/j.carbon.2004.12.027
• Savvatimskiy AI 2009, 'Experimental Electrical Resistivity of Liquid Carbon in the Temperature Range from 4800 to ~20,000 K', Carbon, vol. 47, no. 10, pp. 2322–8, doi:10.1016/j.carbon.2009.04.009
• Schaefer JC 1968, 'Boron' in CA Hampel (ed.), The Encyclopedia of the Chemical Elements, Reinhold, New York, pp. 73–81
• Schauss AG 1991, 'Nephrotoxicity and Neurotoxicity in Humans from Organogermanium Compounds and Germanium Dioxide', Biological Trace Element Research, vol. 29, no. 3, pp. 267–80, doi:10.1007/BF03032683
• Schmidbaur H & Schier A 2008, 'A Briefing on Aurophilicity,' Chemical Society Reviews, vol. 37, pp. 1931–51, doi:10.1039/B708845K
• Schroers J 2013, 'Bulk Metallic Glasses', Physics Today, vol. 66, no. 2, pp. 32–7, doi:10.1063/PT.3.1885
• Schwab GM & Gerlach J 1967, 'The Reaction of Germanium with Molybdenum(VI) Oxide in the Solid State' (in German), Zeitschrift für Physikalische Chemie, vol. 56, pp. 121–132, doi:10.1524/zpch.1967.56.3_4.121
• Schwartz MM 2002, Encyclopedia of Materials, Parts, and Finishes, 2nd ed., CRC Press, Boca Raton, Florida, ISBN 1-56676-661-3
• Schwietzer GK and Pesterfield LL 2010, The Aqueous Chemistry of the Elements, Oxford University, Oxford, ISBN 0-19-539335-X
• ScienceDaily 2012, 'Recharge Your Cell Phone With a Touch? New nanotechnology converts body heat into power', February 22, viewed 13 January 2013
• Scott EC & Kanda FA 1962, The Nature of Atoms and Molecules: A General Chemistry, Harper & Row, New York
• Secrist JH & Powers WH 1966, General Chemistry, D. Van Nostrand, Princeton, New Jersey
• Segal BG 1989, Chemistry: Experiment and Theory, 2nd ed., John Wiley & Sons, New York, ISBN 0-471-84929-4
• Sekhon BS 2012, 'Metalloid Compounds as Drugs', Research in Pharmaceutical Sciences, vol. 8, no. 3, pp. 145–58, ISSN 1735-9414
• Sequeira CAC 2011, 'Copper and Copper Alloys', in R Winston Revie (ed.), Uhlig's Corrosion Handbook, 3rd ed., John Wiley & Sons, Hoboken, New Jersey, pp. 757–86, ISBN 1-118-11003-X
• Sharp DWA 1981, 'Metalloids', in Miall's Dictionary of Chemistry, 5th ed, Longman, Harlow, ISBN 0-582-35152-9
• Sharp DWA 1983, The Penguin Dictionary of Chemistry, 2nd ed., Harmondsworth, Middlesex, ISBN 0-14-051113-X
• Shelby JE 2005, Introduction to Glass Science and Technology, 2nd ed., Royal Society of Chemistry, Cambridge, ISBN 0-85404-639-9
• Sidgwick NV 1950, The Chemical Elements and Their Compounds, vol. 1, Clarendon, Oxford
• Siebring BR 1967, Chemistry, MacMillan, New York
• Siekierski S & Burgess J 2002, Concise Chemistry of the Elements, Horwood, Chichester, ISBN 1-898563-71-3
• Silberberg MS 2006, Chemistry: The Molecular Nature of Matter and Change, 4th ed., McGraw-Hill, New York, ISBN 0-07-111658-3
• Simple Memory Art c. 2005, Periodic Table, EVA vinyl shower curtain, San Francisco
• Skinner GRB, Hartley CE, Millar D & Bishop E 1979, 'Possible Treatment for Cold Sores,' British Medical Journal, vol 2, no. 6192, p. 704, doi:10.1136/bmj.2.6192.704
• Slade S 2006, Elements and the Periodic Table, The Rosen Publishing Group, New York, ISBN 1-4042-2165-4
• Science Learning Hub 2009, 'The Essential Elements', The University of Waikato, viewed 16 January 2013
• Smith DW 1990, Inorganic Substances: A Prelude to the Study of Descriptive Inorganic Chemistry, Cambridge University, Cambridge, ISBN 0-521-33738-0
• Smith R 1994, Conquering Chemistry, 2nd ed., McGraw-Hill, Sydney, ISBN 0-07-470146-0
• Smith AH, Marshall G, Yuan Y, Steinmaus C, Liaw J, Smith MT, Wood L, Heirich M, Fritzemeier RM, Pegram MD & Ferreccio C 2014, 'Rapid Reduction in Breast Cancer Mortality with Inorganic Arsenic in Drinking Water', "EBioMedicine," doi:10.1016/j.ebiom.2014.10.005
• Sneader W 2005, Drug Discovery: A History, John Wiley & Sons, New York, ISBN 0-470-01552-7
• Snyder MK 1966, Chemistry: Structure and Reactions, Holt, Rinehart and Winston, New York
• Soverna S 2004, 'Indication for a Gaseous Element 112', in U Grundinger (ed.), GSI Scientific Report 2003, GSI Report 2004–1, p. 187, ISSN 0174-0814
• Steele D 1966, The Chemistry of the Metallic Elements, Pergamon Press, Oxford
• Stein L 1985, 'New Evidence that Radon is a Metalloid Element: Ion-Exchange Reactions of Cationic Radon', Journal of the Chemical Society, Chemical Communications, vol. 22, pp. 1631–2, doi:10.1039/C39850001631
• Stein L 1987, 'Chemical Properties of Radon' in PK Hopke (ed.) 1987, Radon and its Decay products: Occurrence, Properties, and Health Effects, American Chemical Society, Washington DC, pp. 240–51, ISBN 0-8412-1015-2
• Steudel R 1977, Chemistry of the Non-metals: With an Introduction to atomic Structure and Chemical Bonding, Walter de Gruyter, Berlin, ISBN 3-11-004882-5
• Steurer W 2007, 'Crystal Structures of the Elements' in JW Marin (ed.), Concise Encyclopedia of the Structure of Materials, Elsevier, Oxford, pp. 127–45, ISBN 0-08-045127-6
• Stevens SD & Klarner A 1990, Deadly Doses: A Writer's Guide to Poisons, Writer's Digest Books, Cincinnati, Ohio, ISBN 0-89879-371-8
• Stoker HS 2010, General, Organic, and Biological Chemistry, 5th ed., Brooks/Cole, Cengage Learning, Belmont California, ISBN 0-495-83146-8
• Stott RW 1956, A Companion to Physical and Inorganic Chemistry, Longmans, Green and Co., London
• Stuke J 1974, 'Optical and Electrical Properties of Selenium', in RA Zingaro & WC Cooper (eds), Selenium, Van Nostrand Reinhold, New York, pp. 174–297, ISBN 0-442-29575-8
• Swalin RA 1962, Thermodynamics of Solids, John Wiley & Sons, New York
• Swift EH & Schaefer WP 1962, Qualitative Elemental Analysis, WH Freeman, San Francisco
• Swink LN & Carpenter GB 1966, 'The Crystal Structure of Basic Tellurium Nitrate, Te₂O₄•HNO₃', Acta Crystallographica, vol. 21, no. 4, pp. 578–83, doi:10.1107/S0365110X66003487
• Szpunar J, Bouyssiere B & Lobinski R 2004, 'Advances in Analytical Methods for Speciation of Trace Elements in the Environment', in AV Hirner & H Emons (eds), Organic Metal and Metalloid Species in the Environment: Analysis, Distribution Processes and Toxicological Evaluation, Springer-Verlag, Berlin, pp. 17–40, ISBN 3-540-20829-1
• Taguena-Martinez J, Barrio RA & Chambouleyron I 1991, 'Study of Tin in Amorphous Germanium', in JA Blackman & J Tagüeña (eds), Disorder in Condensed Matter Physics: A Volume in Honour of Roger Elliott, Clarendon Press, Oxford, ISBN 0-19-853938-X, pp. 139–44
• Taniguchi M, Suga S, Seki M, Sakamoto H, Kanzaki H, Akahama Y, Endo S, Terada S & Narita S 1984, 'Core-Exciton Induced Resonant Photoemission in the Covalent Semiconductor Black Phosphorus', Solid State Communications, vo1. 49, no. 9, pp. 867–70
• Tao SH & Bolger PM 1997, 'Hazard Assessment of Germanium Supplements', Regulatory Toxicology and Pharmacology, vol. 25, no. 3, pp. 211–19, doi:10.1006/rtph.1997.1098
• Taylor MD 1960, First Principles of Chemistry, D. Van Nostrand, Princeton, New Jersey
• Thayer JS 1977, 'Teaching Bio-Organometal Chemistry. I. The Metalloids', Journal of Chemical Education, vol. 54, no. 10, pp. 604–6, doi:10.1021/ed054p604
• The Economist 2012, 'Phase-Change Memory: Altered States', Technology Quarterly, September 1
• The American Heritage Science Dictionary 2005, Houghton Mifflin Harcourt, Boston, ISBN 0-618-45504-3
• The Chemical News 1897, 'Notices of Books: A Manual of Chemistry, Theoretical and Practical, by WA Tilden', vol. 75, no. 1951, p. 189
• Thomas S & Visakh PM 2012, Handbook of Engineering and Speciality Thermoplastics: Volume 3: Polyethers and Polyesters, John Wiley & Sons, Hoboken, New Jersey, ISBN 0470639261
• Tilden WA 1876, Introduction to the Study of Chemical Philosophy, D. Appleton and Co., New York
• Timm JA 1944, General Chemistry, McGraw-Hill, New York
• Tyler Miller G 1987, Chemistry: A Basic Introduction, 4th ed., Wadsworth Publishing Company, Belmont, California, ISBN 0-534-06912-6
• Togaya M 2000, 'Electrical Resistivity of Liquid Carbon at High Pressure', in MH Manghnani, W Nellis & MF.Nicol (eds), Science and Technology of High Pressure, proceedings of AIRAPT-17, Honolulu, Hawaii, 25–30 July 1999, vol. 2, Universities Press, Hyderabad, pp. 871–4, ISBN 81-7371-339-1
• Tom LWC, Elden LM & Marsh RR 2004, 'Topical antifungals', in PS Roland & JA Rutka, Ototoxicity, BC Decker, Hamilton, Ontario, pp. 134–9, ISBN 1-55009-263-4
• Tominaga J 2006, 'Application of Ge–Sb–Te Glasses for Ultrahigh Density Optical Storage', in AV Kolobov (ed.), Photo-Induced Metastability in Amorphous Semiconductors, Wiley-VCH, pp. 327–7, ISBN 3-527-60866-4
• Toy AD 1975, The Chemistry of Phosphorus, Pergamon, Oxford, ISBN 0-08-018780-3
• Träger F 2007, Springer Handbook of Lasers and Optics, Springer, New York, ISBN 978-0-387-95579-7
• Traynham JG 1989, 'Carbonium Ion: Waxing and Waning of a Name', Journal of Chemical Education, vol. 63, no. 11, pp. 930–3, doi:10.1021/ed063p930
• Trivedi Y, Yung E & Katz DS 2013, 'Imaging in Fever of Unknown Origin', in BA Cunha (ed.), Fever of Unknown Origin, Informa Healthcare USA, New York, pp. 209–228, ISBN 0-8493-3615-5
• Turner M 2011, 'German E. Coli Outbreak Caused by Previously Unknown Strain', Nature News, 2 Jun, doi:10.1038/news.2011.345
• Turova N 2011, Inorganic Chemistry in Tables, Springer, Heidelberg, ISBN 978-3-642-20486-9
• Tuthill G 2011, 'Faculty profile: Elements of Great Teaching', The Iolani School Bulletin, Winter, viewed 29 October 2011
• Tyler PM 1948, From the Ground Up: Facts and Figures of the Mineral Industries of the United States, McGraw-Hill, New York
• UCR Today 2011, 'Research Performed in Guy Bertrand's Lab Offers Vast Family of New Catalysts for use in Drug Discovery, Biotechnology', University of California, Riverside, July 28
• Uden PC 2005, 'Speciation of Selenium,' in R Cornelis, J Caruso, H Crews & K Heumann (eds), Handbook of Elemental Speciation II: Species in the Environment, Food, Medicine and Occupational Health, John Wiley & Sons, Chichester, pp. 346–65, ISBN 0-470-85598-3
• United Nuclear Scientific 2014, 'Disk Sources, Standard', viewed 5 April 2014
• US Bureau of Naval Personnel 1965, Shipfitter 3 & 2, US Government Printing Office, Washington
• US Environmental Protection Agency 1988, Ambient Aquatic Life Water Quality Criteria for Antimony (III), draft, Office of Research and Development, Environmental Research Laboratories, Washington
• University of Limerick 2014, 'Researchers make breakthrough in battery technology,' 7 February, viewed 2 March 2014
• University of Utah 2014, New 'Topological Insulator' Could Lead to Superfast Computers, Phys.org, viewed 15 December 2014
• Van Muylder J & Pourbaix M 1974, 'Arsenic', in M Pourbaix (ed.), Atlas of Electrochemical Equilibria in Aqueous Solutions, 2nd ed., National Association of Corrosion Engineers, Houston
• Van der Put PJ 1998, The Inorganic Chemistry of Materials: How to Make Things Out of Elements, Plenum, New York, ISBN 0-306-45731-8
• Van Setten MJ, Uijttewaal MA, de Wijs GA & Groot RA 2007, 'Thermodynamic Stability of Boron: The Role of Defects and Zero Point Motion', Journal of the American Chemical Society, vol. 129, no. 9, pp. 2458–65, doi:10.1021/ja0631246
• Vasáros L & Berei K 1985, 'General Properties of Astatine', pp. 107–28, in Kugler & Keller
• Vernon RE 2013, 'Which Elements Are Metalloids?', Journal of Chemical Education, vol. 90, no. 12, pp. 1703–1707, doi:10.1021/ed3008457
• Walker P & Tarn WH 1996, CRC Handbook of Metal Etchants, Boca Raton, FL, ISBN 0849336236
• Walters D 1982, Chemistry, Franklin Watts Science World series, Franklin Watts, London, ISBN 0-531-04581-1
• Wang Y & Robinson GH 2011, 'Building a Lewis Base with Boron', Science, vol. 333, no. 6042, pp. 530–531, doi:10.1126/science.1209588
• Wanga WH, Dongb C & Shek CH 2004, 'Bulk Metallic Glasses', Materials Science and Engineering Reports, vol. 44, nos 2–3, pp. 45–89, doi:10.1016/j.mser.2004.03.001
• Warren J & Geballe T 1981, 'Research Opportunities in New Energy-Related Materials', Materials Science and Engineering, vol. 50, no. 2, pp. 149–98, doi:10.1016/0025-5416(81)90177-4
• Weingart GW 1947, Pyrotechnics, 2nd ed., Chemical Publishing Company, New York
• Wells AF 1984, Structural Inorganic Chemistry, 5th ed., Clarendon, Oxford, ISBN 0-19-855370-6
• Whitten KW, Davis RE, Peck LM & Stanley GG 2007, Chemistry, 8th ed., Thomson Brooks/Cole, Belmont, California, ISBN 0-495-01449-4
• Wiberg N 2001, Inorganic Chemistry, Academic Press, San Diego, ISBN 0-12-352651-5
• Wilkie CA & Morgan AB 2009, Fire Retardancy of Polymeric Materials, CRC Press, Boca Raton, Florida, ISBN 1-4200-8399-6
• Witt AF & Gatos HC 1968, 'Germanium', in CA Hampel (ed.), The Encyclopedia of the Chemical Elements, Reinhold, New York, pp. 237–44
• Wogan T 2014, "First experimental evidence of a boron fullerene", Chemistry World, 14 July
• Woodward WE 1948, Engineering Metallurgy, Constable, London
• WPI-AIM (World Premier Institute – Advanced Institute for Materials Research) 2012, 'Bulk Metallic Glasses: An Unexpected Hybrid', AIMResearch, Tohoku University, Sendai, Japan, 30 April
• Wulfsberg G 2000, Inorganic Chemistry, University Science Books, Sausalito California, ISBN 1-891389-01-7
• Xu Y, Miotkowski I, Liu C, Tian J, Nam H, Alidoust N, Hu J, Shih C-K, Hasan M & Chen YP 2014, 'Observation of Topological Surface State Quantum Hall Effect in an Intrinsic Three-dimensional Topological Insulator,' Nature Physics, vol, 10, pp. 956–963, doi:10.1038/nphys3140
• Yacobi BG & Holt DB 1990, Cathodoluminescence Microscopy of Inorganic Solids, Plenum, New York, ISBN 0-306-43314-1
• Yang K, Setyawan W, Wang S, Nardelli MB & Curtarolo S 2012, 'A Search Model for Topological Insulators with High-throughput Robustness Descriptors,' Nature Materials, vol. 11, pp. 614–619, doi:10.1038/nmat3332
• Yasuda E, Inagaki M, Kaneko K, Endo M, Oya A & Tanabe Y 2003, Carbon Alloys: Novel Concepts to Develop Carbon Science and Technology, Elsevier Science, Oxford, pp. 3–11 et seq, ISBN 0-08-044163-7
• Yetter RA 2012, Nanoengineered Reactive Materials and their Combustion and Synthesis, course notes, Princeton-CEFRC Summer School On Combustion, June 25–29, 2012, Penn State University
• Young RV & Sessine S (eds) 2000, World of Chemistry, Gale Group, Farmington Hills, Michigan, ISBN 0-7876-3650-9
• Young TF, Finley K, Adams WF, Besser J, Hopkins WD, Jolley D, McNaughton E, Presser TS, Shaw DP & Unrine J 2010, 'What You Need to Know About Selenium', in PM Chapman, WJ Adams, M Brooks, CJ Delos, SN Luoma, WA Maher, H Ohlendorf, TS Presser & P Shaw (eds), Ecological Assessment of Selenium in the Aquatic Environment, CRC, Boca Raton, Florida, pp. 7–45, ISBN 1-4398-2677-3
• Zalutsky MR & Pruszynski M 2011, 'Astatine-211: Production and Availability', Current Radiopharmaceuticals, vol. 4, no. 3, pp. 177–185, doi:10.2174/10177
• Zhang GX 2002, 'Dissolution and Structures of Silicon Surface', in MJ Deen, D Misra & J Ruzyllo (eds), Integrated Optoelectronics: Proceedings of the First International Symposium, Philadelphia, PA, The Electrochemical Society, Pennington, NJ, pp. 63–78, ISBN 1-56677-370-9
• Zhang TC, Lai KCK & Surampalli AY 2008, 'Pesticides', in A Bhandari, RY Surampalli, CD Adams, P Champagne, SK Ong, RD Tyagi & TC Zhang (eds), Contaminants of Emerging Environmental Concern, American Society of Civil Engineers, Reston, Virginia, ISBN 978-0-7844-1014-1, pp. 343–415
• Zhdanov GS 1965, Crystal Physics, translated from the Russian publication of 1961 by AF Brown (ed.), Oliver & Boyd, Edinburgh
• Zingaro RA 1994, 'Arsenic: Inorganic Chemistry', in RB King (ed.) 1994, Encyclopedia of Inorganic Chemistry, John Wiley & Sons, Chichester, pp. 192–218, ISBN 0-471-93620-0

Further reading

• Brady JE, Humiston GE & Heikkinen H 1980, 'Chemistry of the Representative Elements: Part II, The Metalloids and Nonmetals', in General Chemistry: Principles and Structure, 2nd ed., SI version, John Wiley & Sons, New York, pp. 537–591, ISBN 0-471-06315-0
• Chedd G 1969, Half-way Elements: The Technology of Metalloids, Doubleday, New York
• Choppin GR & Johnsen RH 1972, 'Group IV and the Metalloids,' in Introductory Chemistry, Addison-Wesley, Reading, Massachusetts, pp. 341–357
• Dunstan S 1968, 'The Metalloids', in Principles of Chemistry, D. Van Nostrand Company, London, pp. 407–39
• Goldsmith RH 1982, 'Metalloids', Journal of Chemical Education, vol. 59, no. 6, pp. 526–527, doi:10.1021/ed059p526
• Hawkes SJ 2001, 'Semimetallicity', Journal of Chemical Education, vol. 78, no. 12, pp. 1686–7, doi:10.1021/ed078p1686
• Metcalfe HC, Williams JE & Castka JF 1974, 'Aluminum and the Metalloids', in Modern Chemistry, Holt, Rinehart and Winston, New York, pp. 538–57, ISBN 0-03-089450-6
• Miller JS 2019, 'Viewpoint: Metalloids—An Electronic Band Structure Perspective', Chemistry–A European Perspective, preprint version, doi:10.1002/chem.201903167
• Moeller T, Bailar JC, Kleinberg J, Guss CO, Castellion ME & Metz C 1989, 'Carbon and the Semiconducting Elements', in Chemistry, with Inorganic Qualitative Analysis, 3rd ed., Harcourt Brace Jovanovich, San Diego, pp. 742–75, ISBN 0-15-506492-4
• Rieske M 1998, 'Metalloids', in Encyclopedia of Earth and Physical Sciences, Marshall Cavendish, New York, vol. 6, pp. 758–9, ISBN 0-7614-0551-8 (set)
• Rochow EG 1966, The Metalloids, DC Heath and Company, Boston
• Vernon RE 2013, 'Which Elements are Metalloids?', Journal of Chemical Education, vol. 90, no. 12, pp. 1703–7, doi:10.1021/ed3008457
• —— 2020, 'Organising the metals and nonmetals', Foundations of chemistry, (open access)