Chemical element

In chemistry, an element is a pure substance which cannot be broken down by chemical means, consisting of atoms which have identical numbers of protons in their atomic nuclei. The number of protons in the nucleus is the defining property of an element, and is referred to as the atomic number (represented by the symbol Z).[1] Chemical elements constitute all of the baryonic matter of the universe.

The periodic table of the chemical elements

In total, 118 elements have been identified. The first 94 occur naturally on Earth, and the remaining 24 are synthetic elements produced in nuclear reactions. Save for unstable radioactive elements (radionuclides) which decay quickly, nearly all of the elements are available industrially in varying amounts.

When different elements are combined, they may produce a chemical reaction and form into compounds due to chemical bonds holding the constituent atoms together. Only a minority of elements are found uncombined as relatively pure native element minerals. Nearly all other naturally-occurring elements appear as compounds or mixtures; for example, atmospheric air is primarily a mixture of the elements nitrogen, oxygen, and argon.

The history of the discovery and use of the elements began with primitive human societies that discovered native minerals like carbon, sulfur, copper and gold (though the concept of a chemical element was not yet understood). Attempts to classify materials such as these resulted in the concepts of classical elements, alchemy, and various similar theories throughout human history.

Much of the modern understanding of elements is attributed to Dmitri Mendeleev, a Russian chemist who published the first recognizable periodic table in 1869. The properties of the chemical elements are summarized in this table, which organizes them by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. The use of the periodic table allows chemists to derive relationships between various elements and predict the behavior of theoretical but undiscovered new ones; the discovery and synthesis of further new elements is an ongoing area of scientific study.

Description

The lightest chemical elements are hydrogen and helium, both created by Big Bang nucleosynthesis during the first 20 minutes of the universe[2] in a ratio of around 3:1 by mass (or 12:1 by number of atoms),[3][4] along with tiny traces of the next two elements, lithium and beryllium. Almost all other elements found in nature were made by various natural methods of nucleosynthesis.[5] On Earth, small amounts of new atoms are naturally produced in nucleogenic reactions, or in cosmogenic processes, such as cosmic ray spallation. New atoms are also naturally produced on Earth as radiogenic daughter isotopes of ongoing radioactive decay processes such as alpha decay, beta decay, spontaneous fission, cluster decay, and other rarer modes of decay.

Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope (except for technetium, element 43 and promethium, element 61, which have no stable isotopes). Isotopes considered stable are those for which no radioactive decay has yet been observed. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected. Some of these elements, notably bismuth (atomic number 83), thorium (atomic number 90), and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy metals before the formation of our Solar System. At over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 (atomic number 83) has the longest known alpha decay half-life of any naturally occurring element, and is almost always considered on par with the 80 stable elements.[6][7] The very heaviest elements (those beyond plutonium, element 94) undergo radioactive decay with half-lives so short that they are not found in nature and must be synthesized.

As of 2010, there are 118 known elements (in this context, "known" means observed well enough, even from just a few decay products, to have been differentiated from other elements).[8][9] Of these 118 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: technetium, atomic number 43; promethium, number 61; astatine, number 85; francium, number 87; neptunium, number 93; and plutonium, number 94. These 94 elements have been detected in the universe at large, in the spectra of stars and also supernovae, where short-lived radioactive elements are newly being made. The first 94 elements have been detected directly on Earth as primordial nuclides present from the formation of the solar system, or as naturally occurring fission or transmutation products of uranium and thorium.

The remaining 24 heavier elements, not found today either on Earth or in astronomical spectra, have been produced artificially: these are all radioactive, with very short half-lives; if any atoms of these elements were present at the formation of Earth, they are extremely likely, to the point of certainty, to have already decayed, and if present in novae have been in quantities too small to have been noted. Technetium was the first purportedly non-naturally occurring element synthesized, in 1937, although trace amounts of technetium have since been found in nature (and also the element may have been discovered naturally in 1925).[10] This pattern of artificial production and later natural discovery has been repeated with several other radioactive naturally occurring rare elements.[11]

List of the elements are available by name, atomic number, density, melting point, boiling point and by symbol, as well as ionization energies of the elements. The nuclides of stable and radioactive elements are also available as a list of nuclides, sorted by length of half-life for those that are unstable. One of the most convenient, and certainly the most traditional presentation of the elements, is in the form of the periodic table, which groups together elements with similar chemical properties (and usually also similar electronic structures).

Atomic number
Main article: Atomic number

The atomic number of an element is equal to the number of protons in each atom, and defines the element.[12] For example, all carbon atoms contain 6 protons in their atomic nucleus; so the atomic number of carbon is 6.[13] Carbon atoms may have different numbers of neutrons; atoms of the same element having different numbers of neutrons are known as isotopes of the element.[14]

The number of protons in the atomic nucleus also determines its electric charge, which in turn determines the number of electrons of the atom in its non-ionized state. The electrons are placed into atomic orbitals that determine the atom's various chemical properties. The number of neutrons in a nucleus usually has very little effect on an element's chemical properties (except in the case of hydrogen and deuterium). Thus, all carbon isotopes have nearly identical chemical properties because they all have six protons and six electrons, even though carbon atoms may, for example, have 6 or 8 neutrons. That is why the atomic number, rather than mass number or atomic weight, is considered the identifying characteristic of a chemical element.

The symbol for atomic number is Z.

Isotopes
Main articles: Isotope, Stable isotope ratio, and List of nuclides

Isotopes are atoms of the same element (that is, with the same number of protons in their atomic nucleus), but having different numbers of neutrons. Thus, for example, there are three main isotopes of carbon. All carbon atoms have 6 protons in the nucleus, but they can have either 6, 7, or 8 neutrons. Since the mass numbers of these are 12, 13 and 14 respectively, the three isotopes of carbon are known as carbon-12, carbon-13, and carbon-14, often abbreviated to 12C, 13C, and 14C. Carbon in everyday life and in chemistry is a mixture of 12C (about 98.9%), 13C (about 1.1%) and about 1 atom per trillion of 14C.

Most (66 of 94) naturally occurring elements have more than one stable isotope. Except for the isotopes of hydrogen (which differ greatly from each other in relative mass—enough to cause chemical effects), the isotopes of a given element are chemically nearly indistinguishable.

All of the elements have some isotopes that are radioactive (radioisotopes), although not all of these radioisotopes occur naturally. The radioisotopes typically decay into other elements upon radiating an alpha or beta particle. If an element has isotopes that are not radioactive, these are termed "stable" isotopes. All of the known stable isotopes occur naturally (see primordial isotope). The many radioisotopes that are not found in nature have been characterized after being artificially made. Certain elements have no stable isotopes and are composed only of radioactive isotopes: specifically the elements without any stable isotopes are technetium (atomic number 43), promethium (atomic number 61), and all observed elements with atomic numbers greater than 82.

Of the 80 elements with at least one stable isotope, 26 have only one single stable isotope. The mean number of stable isotopes for the 80 stable elements is 3.1 stable isotopes per element. The largest number of stable isotopes that occur for a single element is 10 (for tin, element 50).

Isotopic mass and atomic mass
Main articles: atomic mass and relative atomic mass

The mass number of an element, A, is the number of nucleons (protons and neutrons) in the atomic nucleus. Different isotopes of a given element are distinguished by their mass numbers, which are conventionally written as a superscript on the left hand side of the atomic symbol (e.g. 238U). The mass number is always a whole number and has units of "nucleons". For example, magnesium-24 (24 is the mass number) is an atom with 24 nucleons (12 protons and 12 neutrons).

Whereas the mass number simply counts the total number of neutrons and protons and is thus a natural (or whole) number, the atomic mass of a single atom is a real number giving the mass of a particular isotope (or "nuclide") of the element, expressed in atomic mass units (symbol: u). In general, the mass number of a given nuclide differs in value slightly from its atomic mass, since the mass of each proton and neutron is not exactly 1 u; since the electrons contribute a lesser share to the atomic mass as neutron number exceeds proton number; and (finally) because of the nuclear binding energy. For example, the atomic mass of chlorine-35 to five significant digits is 34.969 u and that of chlorine-37 is 36.966 u. However, the atomic mass in u of each isotope is quite close to its simple mass number (always within 1%). The only isotope whose atomic mass is exactly a natural number is 12C, which by definition has a mass of exactly 12 because u is defined as 1/12 of the mass of a free neutral carbon-12 atom in the ground state.

The standard atomic weight (commonly called "atomic weight") of an element is the average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance, relative to the atomic mass unit. This number may be a fraction that is not close to a whole number. For example, the relative atomic mass of chlorine is 35.453 u, which differs greatly from a whole number as it is an average of about 76% chlorine-35 and 24% chlorine-37. Whenever a relative atomic mass value differs by more than 1% from a whole number, it is due to this averaging effect, as significant amounts of more than one isotope are naturally present in a sample of that element.

Chemically pure and isotopically pure

Chemists and nuclear scientists have different definitions of a pure element. In chemistry, a pure element means a substance whose atoms all (or in practice almost all) have the same atomic number, or number of protons. Nuclear scientists, however, define a pure element as one that consists of only one stable isotope.[15]

For example, a copper wire is 99.99% chemically pure if 99.99% of its atoms are copper, with 29 protons each. However it is not isotopically pure since ordinary copper consists of two stable isotopes, 69% 63Cu and 31% 65Cu, with different numbers of neutrons. However, a pure gold ingot would be both chemically and isotopically pure, since ordinary gold consists only of one isotope, 197Au.

Allotropes
Main article: Allotropy

Atoms of chemically pure elements may bond to each other chemically in more than one way, allowing the pure element to exist in multiple chemical structures (spatial arrangements of atoms), known as allotropes, which differ in their properties. For example, carbon can be found as diamond, which has a tetrahedral structure around each carbon atom; graphite, which has layers of carbon atoms with a hexagonal structure stacked on top of each other; graphene, which is a single layer of graphite that is very strong; fullerenes, which have nearly spherical shapes; and carbon nanotubes, which are tubes with a hexagonal structure (even these may differ from each other in electrical properties). The ability of an element to exist in one of many structural forms is known as 'allotropy'.

The standard state, also known as the reference state, of an element is defined as its thermodynamically most stable state at a pressure of 1 bar and a given temperature (typically at 298.15 K). In thermochemistry, an element is defined to have an enthalpy of formation of zero in its standard state. For example, the reference state for carbon is graphite, because the structure of graphite is more stable than that of the other allotropes.

Properties

Several kinds of descriptive categorizations can be applied broadly to the elements, including consideration of their general physical and chemical properties, their states of matter under familiar conditions, their melting and boiling points, their densities, their crystal structures as solids, and their origins.

General properties

Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements. A first distinction is between metals, which readily conduct electricity, nonmetals, which do not, and a small group, (the metalloids), having intermediate properties and often behaving as semiconductors.

A more refined classification is often shown in colored presentations of the periodic table. This system restricts the terms "metal" and "nonmetal" to only certain of the more broadly defined metals and nonmetals, adding additional terms for certain sets of the more broadly viewed metals and nonmetals. The version of this classification used in the periodic tables presented here includes: actinides, alkali metals, alkaline earth metals, halogens, lanthanides, transition metals, post-transition metals, metalloids, reactive nonmetals, and noble gases. In this system, the alkali metals, alkaline earth metals, and transition metals, as well as the lanthanides and the actinides, are special groups of the metals viewed in a broader sense. Similarly, the reactive nonmetals and the noble gases are nonmetals viewed in the broader sense. In some presentations, the halogens are not distinguished, with astatine identified as a metalloid and the others identified as nonmetals.

States of matter

Another commonly used basic distinction among the elements is their state of matter (phase), whether solid, liquid, or gas, at a selected standard temperature and pressure (STP). Most of the elements are solids at conventional temperatures and atmospheric pressure, while several are gases. Only bromine and mercury are liquids at 0 degrees Celsius (32 degrees Fahrenheit) and normal atmospheric pressure; caesium and gallium are solids at that temperature, but melt at 28.4 °C (83.2 °F) and 29.8 °C (85.6 °F), respectively.

Melting and boiling points

Melting and boiling points, typically expressed in degrees Celsius at a pressure of one atmosphere, are commonly used in characterizing the various elements. While known for most elements, either or both of these measurements is still undetermined for some of the radioactive elements available in only tiny quantities. Since helium remains a liquid even at absolute zero at atmospheric pressure, it has only a boiling point, and not a melting point, in conventional presentations.

Densities
Main article: Densities of the elements (data page)

The density at selected standard temperature and pressure (STP) is frequently used in characterizing the elements. Density is often expressed in grams per cubic centimeter (g/cm3). Since several elements are gases at commonly encountered temperatures, their densities are usually stated for their gaseous forms; when liquefied or solidified, the gaseous elements have densities similar to those of the other elements.

When an element has allotropes with different densities, one representative allotrope is typically selected in summary presentations, while densities for each allotrope can be stated where more detail is provided. For example, the three familiar allotropes of carbon (amorphous carbon, graphite, and diamond) have densities of 1.8–2.1, 2.267, and 3.515 g/cm3, respectively.

Crystal structures
Main article: Crystal structure

The elements studied to date as solid samples have eight kinds of crystal structures: cubic, body-centered cubic, face-centered cubic, hexagonal, monoclinic, orthorhombic, rhombohedral, and tetragonal. For some of the synthetically produced transuranic elements, available samples have been too small to determine crystal structures.

Occurrence and origin on Earth

Chemical elements may also be categorized by their origin on Earth, with the first 94 considered naturally occurring, while those with atomic numbers beyond 94 have only been produced artificially as the synthetic products of man-made nuclear reactions.

Of the 94 naturally occurring elements, 83 are considered primordial and either stable or weakly radioactive. The remaining 11 naturally occurring elements possess half lives too short for them to have been present at the beginning of the Solar System, and are therefore considered transient elements. Of these 11 transient elements, 5 (polonium, radon, radium, actinium, and protactinium) are relatively common decay products of thorium and uranium. The remaining 6 transient elements (technetium, promethium, astatine, francium, neptunium, and plutonium) occur only rarely, as products of rare decay modes or nuclear reaction processes involving uranium or other heavy elements.

No radioactive decay has been observed for elements with atomic numbers 1 through 82, except 43 (technetium) and 61 (promethium). Observationally stable isotopes of some elements (such as tungsten and lead), however, are predicted to be slightly radioactive with very long half-lives:[16] for example, the half-lives predicted for the observationally stable lead isotopes range from 1035 to 10189 years. Elements with atomic numbers 43, 61, and 83 through 94 are unstable enough that their radioactive decay can readily be detected. Three of these elements, bismuth (element 83), thorium (element 90), and uranium (element 92) have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy elements before the formation of the Solar System. For example, at over 1.9×1019 years, over a billion times longer than the current estimated age of the universe, bismuth-209 has the longest known alpha decay half-life of any naturally occurring element.[6][7] The very heaviest 24 elements (those beyond plutonium, element 94) undergo radioactive decay with short half-lives and cannot be produced as daughters of longer-lived elements, and thus are not known to occur in nature at all.

Periodic table
Main article: Periodic table
Group 1 2 3   4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Alkali metals Alkaline earth metals Pnicto­gens Chal­co­gens Halo­gens Noble gases
Period

1

 Hydro­gen1H​1.008 He­lium2He​4.0026
2 Lith­ium3Li​6.94 Beryl­lium4Be​9.0122 Boron5B​10.81 Carbon6C​12.011 Nitro­gen7N​14.007 Oxy­gen8O​15.999 Fluor­ine9F​18.998 Neon10Ne​20.180
3 So­dium11Na​22.990 Magne­sium12Mg​24.305 Alumin­ium13Al​26.982 Sili­con14Si​28.085 Phos­phorus15P​30.974 Sulfur16S​32.06 Chlor­ine17Cl​35.45 Argon18Ar​39.95
4 Potas­sium19K​39.098 Cal­cium20Ca​40.078 Scan­dium21Sc​44.956 Tita­nium22Ti​47.867 Vana­dium23V​50.942 Chrom­ium24Cr​51.996 Manga­nese25Mn​54.938 Iron26Fe​55.845 Cobalt27Co​58.933 Nickel28Ni​58.693 Copper29Cu​63.546 Zinc30Zn​65.38 Gallium31Ga​69.723 Germa­nium32Ge​72.630 Arsenic33As​74.922 Sele­nium34Se​78.971 Bromine35Br​79.904 Kryp­ton36Kr​83.798
5 Rubid­ium37Rb​85.468 Stront­ium38Sr​87.62 Yttrium39Y​88.906 Zirco­nium40Zr​91.224 Nio­bium41Nb​92.906 Molyb­denum42Mo​95.95 Tech­netium43Tc​[97] Ruthe­nium44Ru​101.07 Rho­dium45Rh​102.91 Pallad­ium46Pd​106.42 Silver47Ag​107.87 Cad­mium48Cd​112.41 Indium49In​114.82 Tin50Sn​118.71 Anti­mony51Sb​121.76 Tellur­ium52Te​127.60 Iodine53I​126.90 Xenon54Xe​131.29
6 Cae­sium55Cs​132.91 Ba­rium56Ba​137.33 Lan­thanum57La​138.91 Haf­nium72Hf​178.49 Tanta­lum73Ta​180.95 Tung­sten74W​183.84 Rhe­nium75Re​186.21 Os­mium76Os​190.23 Iridium77Ir​192.22 Plat­inum78Pt​195.08 Gold79Au​196.97 Mer­cury80Hg​200.59 Thallium81Tl​204.38 Lead82Pb​207.2 Bis­muth83Bi​208.98 Polo­nium84Po​[209] Asta­tine85At​[210] Radon86Rn​[222]
7 Fran­cium87Fr​[223] Ra­dium88Ra​[226] Actin­ium89Ac​[227] Ruther­fordium104Rf​[267] Dub­nium105Db​[268] Sea­borgium106Sg​[269] Bohr­ium107Bh​[270] Has­sium108Hs​[269] Meit­nerium109Mt​[278] Darm­stadtium110Ds​[281] Roent­genium111Rg​[282] Coper­nicium112Cn​[285] Nihon­ium113Nh​[286] Flerov­ium114Fl​[289] Moscov­ium115Mc​[290] Liver­morium116Lv​[293] Tenness­ine117Ts​[294] Oga­nesson118Og​[294]
Cerium58Ce​140.12 Praseo­dymium59Pr​140.91 Neo­dymium60Nd​144.24 Prome­thium61Pm​[145] Sama­rium62Sm​150.36 Europ­ium63Eu​151.96 Gadolin­ium64Gd​157.25 Ter­bium65Tb​158.93 Dyspro­sium66Dy​162.50 Hol­mium67Ho​164.93 Erbium68Er​167.26 Thulium69Tm​168.93 Ytter­bium70Yb​173.05 Lute­tium71Lu​174.97  
Thor­ium90Th​232.04 Protac­tinium91Pa​231.04 Ura­nium92U​238.03 Neptu­nium93Np​[237] Pluto­nium94Pu​[244] Ameri­cium95Am​[243] Curium96Cm​[247] Berkel­ium97Bk​[247] Califor­nium98Cf​[251] Einstei­nium99Es​[252] Fer­mium100Fm​[257] Mende­levium101Md​[258] Nobel­ium102No​[259] Lawren­cium103Lr​[266]

The properties of the chemical elements are often summarized using the periodic table, which powerfully and elegantly organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties. The current standard table contains 118 confirmed elements as of 2019.

Although earlier precursors to this presentation exist, its invention is generally credited to the Russian chemist Dmitri Mendeleev in 1869, who intended the table to illustrate recurring trends in the properties of the elements. The layout of the table has been refined and extended over time as new elements have been discovered and new theoretical models have been developed to explain chemical behavior.

Use of the periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior. The table has also found wide application in physics, geology, biology, materials science, engineering, agriculture, medicine, nutrition, environmental health, and astronomy. Its principles are especially important in chemical engineering.

Nomenclature and symbols

The various chemical elements are formally identified by their unique atomic numbers, by their accepted names, and by their symbols.

Atomic numbers

The known elements have atomic numbers from 1 through 118, conventionally presented as Arabic numerals. Since the elements can be uniquely sequenced by atomic number, conventionally from lowest to highest (as in a periodic table), sets of elements are sometimes specified by such notation as "through", "beyond", or "from ... through", as in "through iron", "beyond uranium", or "from lanthanum through lutetium". The terms "light" and "heavy" are sometimes also used informally to indicate relative atomic numbers (not densities), as in "lighter than carbon" or "heavier than lead", although technically the weight or mass of atoms of an element (their atomic weights or atomic masses) do not always increase monotonically with their atomic numbers.

Element names

The naming of various substances now known as elements precedes the atomic theory of matter, as names were given locally by various cultures to various minerals, metals, compounds, alloys, mixtures, and other materials, although at the time it was not known which chemicals were elements and which compounds. As they were identified as elements, the existing names for anciently-known elements (e.g., gold, mercury, iron) were kept in most countries. National differences emerged over the names of elements either for convenience, linguistic niceties, or nationalism. For a few illustrative examples: German speakers use "Wasserstoff" (water substance) for "hydrogen", "Sauerstoff" (acid substance) for "oxygen" and "Stickstoff" (smothering substance) for "nitrogen", while English and some romance languages use "sodium" for "natrium" and "potassium" for "kalium", and the French, Italians, Greeks, Portuguese and Poles prefer "azote/azot/azoto" (from roots meaning "no life") for "nitrogen".

For purposes of international communication and trade, the official names of the chemical elements both ancient and more recently recognized are decided by the International Union of Pure and Applied Chemistry (IUPAC), which has decided on a sort of international English language, drawing on traditional English names even when an element's chemical symbol is based on a Latin or other traditional word, for example adopting "gold" rather than "aurum" as the name for the 79th element (Au). IUPAC prefers the British spellings "aluminium" and "caesium" over the U.S. spellings "aluminum" and "cesium", and the U.S. "sulfur" over the British "sulphur". However, elements that are practical to sell in bulk in many countries often still have locally used national names, and countries whose national language does not use the Latin alphabet are likely to use the IUPAC element names.

According to IUPAC, chemical elements are not proper nouns in English; consequently, the full name of an element is not routinely capitalized in English, even if derived from a proper noun, as in californium and einsteinium. Isotope names of chemical elements are also uncapitalized if written out, e.g., carbon-12 or uranium-235. Chemical element symbols (such as Cf for californium and Es for einsteinium), are always capitalized (see below).

In the second half of the twentieth century, physics laboratories became able to produce nuclei of chemical elements with half-lives too short for an appreciable amount of them to exist at any time. These are also named by IUPAC, which generally adopts the name chosen by the discoverer. This practice can lead to the controversial question of which research group actually discovered an element, a question that delayed the naming of elements with atomic number of 104 and higher for a considerable amount of time. (See element naming controversy).

Precursors of such controversies involved the nationalistic namings of elements in the late 19th century. For example, lutetium was named in reference to Paris, France. The Germans were reluctant to relinquish naming rights to the French, often calling it cassiopeium. Similarly, the British discoverer of niobium originally named it columbium, in reference to the New World. It was used extensively as such by American publications before the international standardization (in 1950).

Chemical symbols

Specific chemical elements

Before chemistry became a science, alchemists had designed arcane symbols for both metals and common compounds. These were however used as abbreviations in diagrams or procedures; there was no concept of atoms combining to form molecules. With his advances in the atomic theory of matter, John Dalton devised his own simpler symbols, based on circles, to depict molecules.

The current system of chemical notation was invented by Berzelius. In this typographical system, chemical symbols are not mere abbreviations—though each consists of letters of the Latin alphabet. They are intended as universal symbols for people of all languages and alphabets.

The first of these symbols were intended to be fully universal. Since Latin was the common language of science at that time, they were abbreviations based on the Latin names of metals. Cu comes from cuprum, Fe comes from ferrum, Ag from argentum. The symbols were not followed by a period (full stop) as with abbreviations. Later chemical elements were also assigned unique chemical symbols, based on the name of the element, but not necessarily in English. For example, sodium has the chemical symbol 'Na' after the Latin natrium. The same applies to "Fe" (ferrum) for iron, "Hg" (hydrargyrum) for mercury, "Sn" (stannum) for tin, "Au" (aurum) for gold, "Ag" (argentum) for silver, "Pb" (plumbum) for lead, "Cu" (cuprum) for copper, and "Sb" (stibium) for antimony. "W" (wolfram) for tungsten ultimately derives from German, "K" (kalium) for potassium ultimately from Arabic.

Chemical symbols are understood internationally when element names might require translation. There have sometimes been differences in the past. For example, Germans in the past have used "J" (for the alternate name Jod) for iodine, but now use "I" and "Iod".

The first letter of a chemical symbol is always capitalized, as in the preceding examples, and the subsequent letters, if any, are always lower case (small letters). Thus, the symbols for californium and einsteinium are Cf and Es.

General chemical symbols

There are also symbols in chemical equations for groups of chemical elements, for example in comparative formulas. These are often a single capital letter, and the letters are reserved and not used for names of specific elements. For example, an "X" indicates a variable group (usually a halogen) in a class of compounds, while "R" is a radical, meaning a compound structure such as a hydrocarbon chain. The letter "Q" is reserved for "heat" in a chemical reaction. "Y" is also often used as a general chemical symbol, although it is also the symbol of yttrium. "Z" is also frequently used as a general variable group. "E" is used in organic chemistry to denote an electron-withdrawing group or an electrophile; similarly "Nu" denotes a nucleophile. "L" is used to represent a general ligand in inorganic and organometallic chemistry. "M" is also often used in place of a general metal.

At least two additional, two-letter generic chemical symbols are also in informal usage, "Ln" for any lanthanide element and "An" for any actinide element. "Rg" was formerly used for any rare gas element, but the group of rare gases has now been renamed noble gases and the symbol "Rg" has now been assigned to the element roentgenium.

Isotope symbols

Isotopes are distinguished by the atomic mass number (total protons and neutrons) for a particular isotope of an element, with this number combined with the pertinent element's symbol. IUPAC prefers that isotope symbols be written in superscript notation when practical, for example 12C and 235U. However, other notations, such as carbon-12 and uranium-235, or C-12 and U-235, are also used.

As a special case, the three naturally occurring isotopes of the element hydrogen are often specified as H for 1H (protium), D for 2H (deuterium), and T for 3H (tritium). This convention is easier to use in chemical equations, replacing the need to write out the mass number for each atom. For example, the formula for heavy water may be written D2O instead of 2H2O.

Origin of the elements
Estimated distribution of dark matter and dark energy in the universe. Only the fraction of the mass and energy in the universe labeled "atoms" is composed of chemical elements.

Only about 4% of the total mass of the universe is made of atoms or ions, and thus represented by chemical elements. This fraction is about 15% of the total matter, with the remainder of the matter (85%) being dark matter. The nature of dark matter is unknown, but it is not composed of atoms of chemical elements because it contains no protons, neutrons, or electrons. (The remaining non-matter part of the mass of the universe is composed of the even more mysterious dark energy).

The universe's 94 naturally occurring chemical elements are thought to have been produced by at least four cosmic processes. Most of the hydrogen, helium and a very small quantity of lithium in the universe was produced primordially in the first few minutes of the Big Bang. Other three recurrently occurring later processes are thought to have produced the remaining elements. Stellar nucleosynthesis, an ongoing process inside stars, produces all elements from carbon through iron in atomic number, but little lithium, beryllium, or boron. Elements heavier in atomic number than iron, as heavy as uranium and plutonium, are produced by explosive nucleosynthesis in supernovas and other cataclysmic cosmic events. Cosmic ray spallation (fragmentation) of carbon, nitrogen, and oxygen is important to the production of lithium, beryllium and boron.

During the early phases of the Big Bang, nucleosynthesis of hydrogen nuclei resulted in the production of hydrogen-1 (protium, 1H) and helium-4 (4He), as well as a smaller amount of deuterium (2H) and very minuscule amounts (on the order of 10−10) of lithium and beryllium. Even smaller amounts of boron may have been produced in the Big Bang, since it has been observed in some very old stars, while carbon has not.[19] It is generally agreed that no heavier elements than boron were produced in the Big Bang. As a result, the primordial abundance of atoms (or ions) consisted of roughly 75% 1H, 25% 4He, and 0.01% deuterium, with only tiny traces of lithium, beryllium, and perhaps boron.[20] Subsequent enrichment of galactic halos occurred due to stellar nucleosynthesis and supernova nucleosynthesis.[21] However, the element abundance in intergalactic space can still closely resemble primordial conditions, unless it has been enriched by some means.

Periodic table showing the cosmogenic origin of each element in the Big Bang, or in large or small stars. Small stars can produce certain elements up to sulfur, by the alpha process. Supernovae are needed to produce "heavy" elements (those beyond iron and nickel) rapidly by neutron buildup, in the r-process. Certain large stars slowly produce other elements heavier than iron, in the s-process; these may then be blown into space in the off-gassing of planetary nebulae

On Earth (and elsewhere), trace amounts of various elements continue to be produced from other elements as products of nuclear transmutation processes. These include some produced by cosmic rays or other nuclear reactions (see cosmogenic and nucleogenic nuclides), and others produced as decay products of long-lived primordial nuclides.[22] For example, trace (but detectable) amounts of carbon-14 (14C) are continually produced in the atmosphere by cosmic rays impacting nitrogen atoms, and argon-40 (40Ar) is continually produced by the decay of primordially occurring but unstable potassium-40 (40K). Also, three primordially occurring but radioactive actinides, thorium, uranium, and plutonium, decay through a series of recurrently produced but unstable radioactive elements such as radium and radon, which are transiently present in any sample of these metals or their ores or compounds. Three other radioactive elements, technetium, promethium, and neptunium, occur only incidentally in natural materials, produced as individual atoms by nuclear fission of the nuclei of various heavy elements or in other rare nuclear processes.

Human technology has produced various additional elements beyond these first 94, with those through atomic number 118 now known.

Abundance
Main article: Abundance of the chemical elements

The following graph (note log scale) shows the abundance of elements in our Solar System. The table shows the twelve most common elements in our galaxy (estimated spectroscopically), as measured in parts per million, by mass.[23] Nearby galaxies that have evolved along similar lines have a corresponding enrichment of elements heavier than hydrogen and helium. The more distant galaxies are being viewed as they appeared in the past, so their abundances of elements appear closer to the primordial mixture. As physical laws and processes appear common throughout the visible universe, however, scientist expect that these galaxies evolved elements in similar abundance.

The abundance of elements in the Solar System is in keeping with their origin from nucleosynthesis in the Big Bang and a number of progenitor supernova stars. Very abundant hydrogen and helium are products of the Big Bang, but the next three elements are rare since they had little time to form in the Big Bang and are not made in stars (they are, however, produced in small quantities by the breakup of heavier elements in interstellar dust, as a result of impact by cosmic rays). Beginning with carbon, elements are produced in stars by buildup from alpha particles (helium nuclei), resulting in an alternatingly larger abundance of elements with even atomic numbers (these are also more stable). In general, such elements up to iron are made in large stars in the process of becoming supernovas. Iron-56 is particularly common, since it is the most stable element that can easily be made from alpha particles (being a product of decay of radioactive nickel-56, ultimately made from 14 helium nuclei). Elements heavier than iron are made in energy-absorbing processes in large stars, and their abundance in the universe (and on Earth) generally decreases with their atomic number.

The abundance of the chemical elements on Earth varies from air to crust to ocean, and in various types of life. The abundance of elements in Earth's crust differs from that in the Solar System (as seen in the Sun and heavy planets like Jupiter) mainly in selective loss of the very lightest elements (hydrogen and helium) and also volatile neon, carbon (as hydrocarbons), nitrogen and sulfur, as a result of solar heating in the early formation of the solar system. Oxygen, the most abundant Earth element by mass, is retained on Earth by combination with silicon. Aluminum at 8% by mass is more common in the Earth's crust than in the universe and solar system, but the composition of the far more bulky mantle, which has magnesium and iron in place of aluminum (which occurs there only at 2% of mass) more closely mirrors the elemental composition of the solar system, save for the noted loss of volatile elements to space, and loss of iron which has migrated to the Earth's core.

The composition of the human body, by contrast, more closely follows the composition of seawater—save that the human body has additional stores of carbon and nitrogen necessary to form the proteins and nucleic acids, together with phosphorus in the nucleic acids and energy transfer molecule adenosine triphosphate (ATP) that occurs in the cells of all living organisms. Certain kinds of organisms require particular additional elements, for example the magnesium in chlorophyll in green plants, the calcium in mollusc shells, or the iron in the hemoglobin in vertebrate animals' red blood cells.

Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers (the Oddo-Harkins rule), and (2) a general decrease in abundance as elements become heavier. Iron is especially common because it represents the minimum energy nuclide that can be made by fusion of helium in supernovae.
Elements in our galaxyParts per million
by mass
Hydrogen 739,000
Helium 240,000
Oxygen 10,400
Carbon 4,600
Neon 1,340
Iron 1,090
Nitrogen 960
Silicon 650
Magnesium 580
Sulfur 440
Potassium 210
Nickel 100
Nutritional elements in the periodic table[24]
H   He
Li Be   B C N O F Ne
Na Mg   Al Si P S Cl Ar
K Ca Sc   Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y   Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac ** Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og
 
  * Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
  ** Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Legend:
 The four basic organic elements
 Quantity elements
 Essential trace elements
 Deemed essential trace element by U.S., not by European Union
 Suggested function from deprivation effects or active metabolic handling, but no clearly-identified biochemical function in humans
 Limited circumstantial evidence for trace benefits or biological action in mammals
 No evidence for biological action in mammals, but essential in some lower organisms.
(In the case of lanthanum, the definition of an essential nutrient as being indispensable and irreplaceable is not completely applicable due to the extreme similarity of the lanthanides. The stable early lanthanides up to Sm are known to stimulate the growth of various lanthanide-using organisms.)[25]

History
Mendeleev's 1869 periodic table: An experiment on a system of elements. Based on their atomic weights and chemical similarities.

Evolving definitions

The concept of an "element" as an undivisible substance has developed through three major historical phases: Classical definitions (such as those of the ancient Greeks), chemical definitions, and atomic definitions.

Classical definitions

Ancient philosophy posited a set of classical elements to explain observed patterns in nature. These elements originally referred to earth, water, air and fire rather than the chemical elements of modern science.

The term 'elements' (stoicheia) was first used by the Greek philosopher Plato in about 360 BCE in his dialogue Timaeus, which includes a discussion of the composition of inorganic and organic bodies and is a speculative treatise on chemistry. Plato believed the elements introduced a century earlier by Empedocles were composed of small polyhedral forms: tetrahedron (fire), octahedron (air), icosahedron (water), and cube (earth).[26][27]

Aristotle, c. 350 BCE, also used the term stoicheia and added a fifth element called aether, which formed the heavens. Aristotle defined an element as:

Element – one of those bodies into which other bodies can decompose, and that itself is not capable of being divided into other.[28]

Chemical definitions

In 1661, Robert Boyle proposed his theory of corpuscularism which favoured the analysis of matter as constituted by irreducible units of matter (atoms) and, choosing to side with neither Aristotle's view of the four elements nor Paracelsus' view of three fundamental elements, left open the question of the number of elements.[29] The first modern list of chemical elements was given in Antoine Lavoisier's 1789 Elements of Chemistry, which contained thirty-three elements, including light and caloric.[30] By 1818, Jöns Jakob Berzelius had determined atomic weights for forty-five of the forty-nine then-accepted elements. Dmitri Mendeleev had sixty-six elements in his periodic table of 1869.

Dmitri Mendeleev

From Boyle until the early 20th century, an element was defined as a pure substance that could not be decomposed into any simpler substance.[29] Put another way, a chemical element cannot be transformed into other chemical elements by chemical processes. Elements during this time were generally distinguished by their atomic weights, a property measurable with fair accuracy by available analytical techniques.

Atomic definitions
Henry Moseley

The 1913 discovery by English physicist Henry Moseley that the nuclear charge is the physical basis for an atom's atomic number, further refined when the nature of protons and neutrons became appreciated, eventually led to the current definition of an element based on atomic number (number of protons per atomic nucleus). The use of atomic numbers, rather than atomic weights, to distinguish elements has greater predictive value (since these numbers are integers), and also resolves some ambiguities in the chemistry-based view due to varying properties of isotopes and allotropes within the same element. Currently, IUPAC defines an element to exist if it has isotopes with a lifetime longer than the 10−14 seconds it takes the nucleus to form an electronic cloud.[31]

By 1914, seventy-two elements were known, all naturally occurring.[32] The remaining naturally occurring elements were discovered or isolated in subsequent decades, and various additional elements have also been produced synthetically, with much of that work pioneered by Glenn T. Seaborg. In 1955, element 101 was discovered and named mendelevium in honor of D.I. Mendeleev, the first to arrange the elements in a periodic manner. Most recently, the synthesis of element 118 (since named oganesson) was reported in October 2006, and the synthesis of element 117 (tennessine) was reported in April 2010.[33]

Discovery and recognition of various elements

Ten materials familiar to various prehistoric cultures are now known to be chemical elements: Carbon, copper, gold, iron, lead, mercury, silver, sulfur, tin, and zinc. Three additional materials now accepted as elements, arsenic, antimony, and bismuth, were recognized as distinct substances prior to 1500 AD. Phosphorus, cobalt, and platinum were isolated before 1750.

Most of the remaining naturally occurring chemical elements were identified and characterized by 1900, including:

Elements isolated or produced since 1900 include:

Recently discovered elements

The first transuranium element (element with atomic number greater than 92) discovered was neptunium in 1940. Since 1999 claims for the discovery of new elements have been considered by the IUPAC/IUPAP Joint Working Party. As of January 2016, all 118 elements have been confirmed as discovered by IUPAC. The discovery of element 112 was acknowledged in 2009, and the name copernicium and the atomic symbol Cn were suggested for it.[34] The name and symbol were officially endorsed by IUPAC on 19 February 2010.[35] The heaviest element that is believed to have been synthesized to date is element 118, oganesson, on 9 October 2006, by the Flerov Laboratory of Nuclear Reactions in Dubna, Russia.[9][36] Tennessine, element 117 was the latest element claimed to be discovered, in 2009.[37] On 28 November 2016, scientists at the IUPAC officially recognized the names for four of the newest chemical elements, with atomic numbers 113, 115, 117, and 118.[38][39]

List of the 118 known chemical elements

The following sortable table shows the 118 known chemical elements.

  • Atomic number, name, and symbol all serve independently as unique identifiers.
  • Names are those accepted by IUPAC.
  • Group, period, and block refer to an element's position in the periodic table. Group numbers here show the currently accepted numbering; for older alternate numberings, see Group (periodic table).
  • State of matter (solid, liquid, or gas) applies at standard temperature and pressure conditions (STP).
  • Occurrence, as indicated by a footnote adjacent to the element's name, distinguishes naturally occurring elements, categorized as either primordial or transient (from decay), and additional synthetic elements that have been produced technologically, but are not known to occur naturally.
  • Color specifies an element's properties using the broad categories commonly presented in periodic tables: Actinide, alkali metal, alkaline earth metal, lanthanide, post-transition metal, metalloid, noble gas, polyatomic or diatomic nonmetal, and transition metal.
List of chemical elements
Atomic number Symbol Element Etymology[40][41] Group Period Atomic weight[42][43] Density Melting point[44] Boiling point Specific heat capacity Electro­negativity Abundance in Earth's crust[upper-roman 1]
(Da) (g/cm3) (K) (K) (J/g · K) (mg/kg)
 
1HHydrogenGreek elements hydro- and -gen, 'water-forming'111.008[upper-roman 2][upper-roman 3][upper-roman 4][upper-roman 5]0.0000898814.0120.2814.3042.201400
2HeHeliumGreek hḗlios, 'sun'1814.002602(2)[upper-roman 2][upper-roman 4]0.0001785—[upper-roman 6]4.225.193–0.008
3LiLithiumGreek líthos, 'stone'126.94[upper-roman 2][upper-roman 3][upper-roman 4][upper-roman 7][upper-roman 5]0.534453.6915603.5820.9820
4BeBerylliumBeryl, a mineral (ultimately from the name of Belur in southern India)229.0121831(5)1.85156027421.8251.572.8
5BBoronBorax, a mineral (from Arabic bawraq)13210.81[upper-roman 2][upper-roman 3][upper-roman 4][upper-roman 5]2.34234942001.0262.0410
6CCarbonLatin carbo, 'coal'14212.011[upper-roman 2][upper-roman 4][upper-roman 5]2.267>4000 (pressure dependent)43000.7092.55200
7NNitrogenGreek nítron and -gen, 'niter-forming'15214.007[upper-roman 2][upper-roman 4][upper-roman 5]0.001250663.1577.361.043.0419
8OOxygenGreek oxy- and -gen, 'acid-forming'16215.999[upper-roman 2][upper-roman 4][upper-roman 5]0.00142954.3690.200.9183.44461000
9FFluorineLatin fluere, 'to flow'17218.998403163(6)0.00169653.5385.030.8243.98585
10NeNeonGreek néon, 'new'18220.1797(6)[upper-roman 2][upper-roman 3]0.000899924.5627.071.03–0.005
11NaSodiumEnglish soda (the symbol Na is derived from New Latin natrium, coined from German Natron, 'natron')1322.98976928(2)0.971370.8711561.2280.9323600
12MgMagnesiumMagnesia, a district of Eastern Thessaly in Greece2324.305[upper-roman 5]1.73892313631.0231.3123300
13AlAluminiumalumina, from Latin alumen (gen. aluminis), 'bitter salt, alum'13326.9815384(3)2.698933.4727920.8971.6182300
14SiSiliconLatin silex, 'flint' (originally silicium)14328.085[upper-roman 4][upper-roman 5]2.3296168735380.7051.9282000
15PPhosphorusGreek phōsphóros, 'light-bearing'15330.973761998(5)1.82317.305500.7692.191050
16SSulfurLatin sulphur, 'brimstone'16332.06[upper-roman 2][upper-roman 4][upper-roman 5]2.067388.36717.870.712.58350
17ClChlorineGreek chlōrós, 'greenish yellow'17335.45[upper-roman 2][upper-roman 3][upper-roman 4][upper-roman 5]0.003214171.6239.110.4793.16145
18ArArgonGreek argós, 'idle' (because of its inertness)18339.95[upper-roman 2][upper-roman 4][upper-roman 5]0.001783783.8087.300.52–3.5
19KPotassiumNew Latin potassa, 'potash' (the symbol K is derived from Latin kalium)1439.0983(1)0.862336.5310320.7570.8220900
20CaCalciumLatin calx, 'lime'2440.078(4)[upper-roman 2]1.54111517570.647141500
21ScScandiumLatin Scandia, 'Scandinavia'3444.955908(5)2.989181431090.5681.3622
22TiTitaniumTitans, the sons of the Earth goddess of Greek mythology4447.867(1)4.54194135600.5231.545650
23VVanadiumVanadis, an Old Norse name for the Scandinavian goddess Freyja5450.9415(1)6.11218336800.4891.63120
24CrChromiumGreek chróma, 'colour'6451.9961(6)7.15218029440.4491.66102
25MnManganeseCorrupted from magnesia negra; see Magnesium7454.938043(2)7.44151923340.4791.55950
26FeIronEnglish word (the symbol Fe is derived from Latin ferrum)8455.845(2)7.874181131340.4491.8356300
27CoCobaltGerman Kobold, 'goblin'9458.933194(3)8.86176832000.4211.8825
28NiNickelNickel, a mischievous sprite of German miner mythology10458.6934(4)8.912172831860.4441.9184
29CuCopperEnglish word, from Latin cuprum, from Ancient Greek Kýpros 'Cyprus'11463.546(3)[upper-roman 4]8.961357.7728350.3851.960
30ZnZincMost likely from German Zinke, 'prong' or 'tooth', though some suggest Persian sang, 'stone'12465.38(2)7.134692.8811800.3881.6570
31GaGalliumLatin Gallia, 'France'13469.723(1)5.907302.914626730.3711.8119
32GeGermaniumLatin Germania, 'Germany'14472.630(8)5.3231211.4031060.322.011.5
33AsArsenicFrench arsenic, from Greek arsenikón 'yellow arsenic' (influenced by arsenikós, 'masculine' or 'virile'), from a West Asian wanderword ultimately from Old Iranian *zarniya-ka, 'golden'15474.921595(6)5.7761090[upper-roman 8]8870.3292.181.8
34SeSeleniumGreek selḗnē, 'moon'16478.971(8)[upper-roman 4]4.8094539580.3212.550.05
35BrBromineGreek brômos, 'stench'17479.904[upper-roman 5]3.122265.8332.00.4742.962.4
36KrKryptonGreek kryptós, 'hidden'18483.798(2)[upper-roman 2][upper-roman 3]0.003733115.79119.930.24831×10−4
37RbRubidiumLatin rubidus, 'deep red'1585.4678(3)[upper-roman 2]1.532312.469610.3630.8290
38SrStrontiumStrontian, a village in Scotland2587.62(1)[upper-roman 2][upper-roman 4]2.64105016550.3010.95370
39YYttriumYtterby, Sweden, where it was found3588.90584(1)4.469179936090.2981.2233
40ZrZirconiumZircon, a mineral4591.224(2)[upper-roman 2]6.506212846820.2781.33165
41NbNiobiumNiobe, daughter of king Tantalus from Greek mythology5592.90637(1)8.57275050170.2651.620
42MoMolybdenumGreek molýbdaina, 'piece of lead', from mólybdos, 'lead', due to confusion with lead ore galena (PbS)6595.95(1)[upper-roman 2]10.22289649120.2512.161.2
43TcTechnetiumGreek tekhnētós, 'artificial'75[98][upper-roman 9]11.524304538–1.9~ 3×10−9[upper-roman 10]
44RuRutheniumNew Latin Ruthenia, 'Russia'85101.07(2)[upper-roman 2]12.37260744230.2382.20.001
45RhRhodiumGreek rhodóeis, 'rose-coloured', from rhódon, 'rose'95102.90549(2)12.41223739680.2432.280.001
46PdPalladiumAsteroid Pallas, considered a planet at the time105106.42(1)[upper-roman 2]12.021828.0532360.2442.20.015
47AgSilverEnglish word (The symbol is derived from Latin argentum)115107.8682(2)[upper-roman 2]10.5011234.9324350.2351.930.075
48CdCadmiumNew Latin cadmia, from King Kadmos125112.414(4)[upper-roman 2]8.69594.2210400.2321.690.159
49InIndiumLatin indicum, 'indigo' (colour found in its spectrum)135114.818(1)7.31429.7523450.2331.780.25
50SnTinEnglish word (The symbol is derived from Latin stannum)145118.710(7)[upper-roman 2]7.287505.0828750.2281.962.3
51SbAntimonyLatin antimonium, the origin of which is uncertain: folk etymologies suggest it is derived from Greek antí ('against') + mónos ('alone'), or Old French anti-moine, 'Monk's bane', but it could plausibly be from or related to Arabic ʾiṯmid, 'antimony', reformatted as a Latin word. (The symbol is derived from Latin stibium 'stibnite'.)155121.760(1)[upper-roman 2]6.685903.7818600.2072.050.2
52TeTelluriumLatin tellus, 'the ground, earth'165127.60(3)[upper-roman 2]6.232722.6612610.2022.10.001
53IIodineFrench iode, from Greek ioeidḗs, 'violet'175126.90447(3)4.93386.85457.40.2142.660.45
54XeXenonGreek xénon, neuter form of xénos 'strange'185131.293(6)[upper-roman 2][upper-roman 3]0.005887161.4165.030.1582.63×10−5
55CsCaesiumLatin caesius, 'sky-blue'16132.90545196(6)1.873301.599440.2420.793
56BaBariumGreek barýs, 'heavy'26137.327(7)3.594100021700.2040.89425
57LaLanthanumGreek lanthánein, 'to lie hidden'36138.90547(7)[upper-roman 2]6.145119337370.1951.139
58CeCeriumDwarf planet Ceres, considered a planet at the time6140.116(1)[upper-roman 2]6.77106837160.1921.1266.5
59PrPraseodymiumGreek prásios dídymos, 'green twin'6140.90766(1)6.773120837930.1931.139.2
60NdNeodymiumGreek néos dídymos, 'new twin'6144.242(3)[upper-roman 2]7.007129733470.191.1441.5
61PmPromethiumPrometheus of Greek mythology6[145][upper-roman 9]7.2613153273–1.132×10−19[upper-roman 10]
62SmSamariumSamarskite, a mineral named after Colonel Vasili Samarsky-Bykhovets, Russian mine official6150.36(2)[upper-roman 2]7.52134520670.1971.177.05
63EuEuropiumEurope6151.964(1)[upper-roman 2]5.243109918020.1821.22
64GdGadoliniumGadolinite, a mineral named after Johan Gadolin, Finnish chemist, physicist and mineralogist6157.25(3)[upper-roman 2]7.895158535460.2361.26.2
65TbTerbiumYtterby, Sweden, where it was found6158.925354(8)8.229162935030.1821.21.2
66DyDysprosiumGreek dysprósitos, 'hard to get'6162.500(1)[upper-roman 2]8.55168028400.171.225.2
67HoHolmiumNew Latin Holmia, 'Stockholm'6164.930328(7)8.795173429930.1651.231.3
68ErErbiumYtterby, Sweden, where it was found6167.259(3)[upper-roman 2]9.066180231410.1681.243.5
69TmThuliumThule, the ancient name for an unclear northern location6168.934218(6)9.321181822230.161.250.52
70YbYtterbiumYtterby, Sweden, where it was found6173.045(10)[upper-roman 2]6.965109714690.1551.13.2
71LuLutetiumLatin Lutetia, 'Paris'6174.9668(1)[upper-roman 2]9.84192536750.1541.270.8
72HfHafniumNew Latin Hafnia, 'Copenhagen' (from Danish havn)46178.49(2)13.31250648760.1441.33
73TaTantalumKing Tantalus, father of Niobe from Greek mythology56180.94788(2)16.654329057310.141.52
74WTungstenSwedish tung sten, 'heavy stone' (The symbol W is from Wolfram, a name used for the element in many languages, originally from Middle High German wolf-rahm (wolf's foam) describing the mineral wolframite)[45] 66183.84(1)19.25369558280.1322.361.3
75ReRheniumLatin Rhenus, 'the Rhine'76186.207(1)21.02345958690.1371.97×10−4
76OsOsmiumGreek osmḗ, 'smell'86190.23(3)[upper-roman 2]22.61330652850.132.20.002
77IrIridiumIris, the Greek goddess of the rainbow96192.217(2)22.56271947010.1312.20.001
78PtPlatinumSpanish platina, 'little silver', from plata 'silver'106195.084(9)21.462041.440980.1332.280.005
79AuGoldEnglish word (the symbol Au is derived from Latin aurum)116196.966570(4)19.2821337.3331290.1292.540.004
80HgMercuryMercury, Roman god of commerce, communication, and luck, known for his speed and mobility (the symbol Hg derives from the element's Latin name hydrargyrum, from Greek hydrárgyros, 'water-silver')126200.592(3)13.5336234.43629.880.1420.085
81TlThalliumGreek thallós, 'green shoot or twig'136204.38[upper-roman 5]11.8557717460.1291.620.85
82PbLeadEnglish word (the symbol Pb is derived from Latin plumbum)146207.2(1)[upper-roman 2][upper-roman 4]11.342600.6120220.1291.8714
83BiBismuthGerman Wismut, from weiß Masse 'white mass', unless from Arabic156208.98040(1)[upper-roman 9]9.807544.718370.1222.020.009
84PoPoloniumLatin Polonia, 'Poland' (the home country of Marie Curie)166[209][upper-roman 9]9.325271235–2.02×10−10[upper-roman 10]
85AtAstatineGreek ástatos, 'unstable'176[210][upper-roman 9]7575610–2.23×10−20[upper-roman 10]
86RnRadonRadium emanation, originally the name of the isotope Radon-222.186[222][upper-roman 9]0.00973202211.30.0942.24×10−13[upper-roman 10]
87FrFranciumFrance17[223][upper-roman 9]1.87281890–0.7~ 1×10−18[upper-roman 10]
88RaRadiumFrench radium, from Latin radius, 'ray'27[226][upper-roman 9]5.597320100.0940.99×10−7[upper-roman 10]
89AcActiniumGreek aktís, 'ray'37[227][upper-roman 9]10.07132334710.121.15.5×10−10[upper-roman 10]
90ThThoriumThor, the Scandinavian god of thunder7232.0377(4)[upper-roman 9][upper-roman 2]11.72211550610.1131.39.6
91PaProtactiniumProto- (from Greek prôtos, 'first, before') + actinium, since actinium is produced through the radioactive decay of protactinium7231.03588(1)[upper-roman 9]15.3718414300–1.51.4×10−6[upper-roman 10]
92UUraniumUranus, the seventh planet in the Solar System7238.02891(3)[upper-roman 9]18.951405.344040.1161.382.7
93NpNeptuniumNeptune, the eighth planet in the Solar System7[237][upper-roman 9]20.459174273–1.36≤ 3×10−12[upper-roman 10]
94PuPlutoniumDwarf planet Pluto, considered the ninth planet in the Solar System at the time7[244][upper-roman 9]19.84912.53501–1.28≤ 3×10−11[upper-roman 10]
95AmAmericiumThe Americas, as the element was first synthesised on the continent, by analogy with europium7[243][upper-roman 9]13.6914492880–1.130[upper-roman 11]
96CmCuriumPierre Curie and Marie Curie, French physicists and chemists7[247][upper-roman 9]13.5116133383–1.280[upper-roman 11]
97BkBerkeliumBerkeley, California, where the element was first synthesised, by analogy with terbium7[247][upper-roman 9]14.7912592900–1.30[upper-roman 11]
98CfCaliforniumCalifornia, where the element was first synthesised7[251][upper-roman 9]15.11173(1743)[upper-roman 12]–1.30[upper-roman 11]
99EsEinsteiniumAlbert Einstein, German physicist7[252][upper-roman 9]8.841133(1269)[upper-roman 12]–1.30[upper-roman 11]
100FmFermiumEnrico Fermi, Italian physicist7[257][upper-roman 9](9.7)[upper-roman 12](1125)[upper-roman 12]––1.30[upper-roman 11]
101MdMendeleviumDmitri Mendeleev, Russian chemist and inventor who proposed the periodic table7[258][upper-roman 9](10.3)[upper-roman 12](1100)[upper-roman 12]––1.30[upper-roman 11]
102NoNobeliumAlfred Nobel, Swedish chemist and engineer7[259][upper-roman 9](9.9)[upper-roman 12](1100)[upper-roman 12]––1.30[upper-roman 11]
103LrLawrenciumErnest Lawrence, American physicist7[266][upper-roman 9](15.6)[upper-roman 12](1900)[upper-roman 12]––1.30[upper-roman 11]
104RfRutherfordiumErnest Rutherford, chemist and physicist from New Zealand47[267][upper-roman 9](23.2)[upper-roman 12](2400)[upper-roman 12](5800)[upper-roman 12]––0[upper-roman 11]
105DbDubniumDubna, Russia, where the Joint Institute for Nuclear Research is located57[268][upper-roman 9](29.3)[upper-roman 12]––––0[upper-roman 11]
106SgSeaborgiumGlenn T. Seaborg, American chemist67[269][upper-roman 9](35.0)[upper-roman 12]––––0[upper-roman 11]
107BhBohriumNiels Bohr, Danish physicist77[270][upper-roman 9](37.1)[upper-roman 12]––––0[upper-roman 11]
108HsHassiumNew Latin Hassia, 'Hesse' (a state in Germany)87[270][upper-roman 9](40.7)[upper-roman 12]––––0[upper-roman 11]
109MtMeitneriumLise Meitner, Austrian physicist97[278][upper-roman 9](37.4)[upper-roman 12]––––0[upper-roman 11]
110DsDarmstadtiumDarmstadt, Germany, where the element was first synthesised107[281][upper-roman 9](34.8)[upper-roman 12]––––0[upper-roman 11]
111RgRoentgeniumWilhelm Conrad Röntgen, German physicist117[282][upper-roman 9](28.7)[upper-roman 12]––––0[upper-roman 11]
112CnCoperniciumNicolaus Copernicus, Polish astronomer127[285][upper-roman 9](14.0)[upper-roman 12](283)[upper-roman 13](340)[upper-roman 13]––0[upper-roman 11]
113NhNihoniumJapanese Nihon, 'Japan' (where the element was first synthesised)137[286][upper-roman 9](16)[upper-roman 12](700)[upper-roman 12](1400)[upper-roman 12]––0[upper-roman 11]
114FlFleroviumFlerov Laboratory of Nuclear Reactions, part of JINR, where the element was synthesised; itself named after Georgy Flyorov, Russian physicist147[289][upper-roman 9](14)[upper-roman 12]–~210––0[upper-roman 11]
115McMoscoviumMoscow Oblast, Russia, where the element was first synthesised157[290][upper-roman 9](13.5)[upper-roman 12](700)[upper-roman 12](1400)[upper-roman 12]––0[upper-roman 11]
116LvLivermoriumLawrence Livermore National Laboratory in Livermore, California, which collaborated with JINR on its synthesis167[293][upper-roman 9](12.9)[upper-roman 12](700)[upper-roman 12](1100)[upper-roman 12]––0[upper-roman 11]
117TsTennessineTennessee, United States (where Oak Ridge National Laboratory is located)177[294][upper-roman 9](7.2)[upper-roman 12](700)[upper-roman 12](883)[upper-roman 12]––0[upper-roman 11]
118OgOganessonYuri Oganessian, Russian-born Armenian physicist187[294][upper-roman 9](5.0)[upper-roman 12][upper-roman 14](320)[upper-roman 12](~350)[upper-roman 12][upper-roman 15]––0[upper-roman 11]

Notes

  1. Unless otherwise indicated, elements are primordial – they occur naturally, and not through decay.
  2. The isotopic composition of this element varies in some geological specimens, and the variation may exceed the uncertainty stated in the table.
  3. The isotopic composition of the element can vary in commercial materials, which can cause the atomic weight to deviate significantly from the given value.
  4. The isotopic composition varies in terrestrial material such that a more precise atomic weight can not be given.
  5. The value listed is the conventional atomic-weight value suitable for trade and commerce. The actual value may differ depending on the isotopic composition of the sample. Since 2009, IUPAC provides the standard atomic-weight values for these elements using the interval notation. The corresponding standard atomic weights are:
    • Hydrogen: [1.00784, 1.00811]
    • Lithium: [6.938, 6.997]
    • Boron: [10.806, 10.821]
    • Carbon: [12.0096, 12.0116]
    • Nitrogen: [14.00643, 14.00728]
    • Oxygen: [15.99903, 15.99977]
    • Magnesium: [24.304, 24.307]
    • Silicon: [28.084, 28.086]
    • Sulfur: [32.059, 32.076]
    • Chlorine: [35.446, 35.457]
    • Argon: [39.792, 39.963]
    • Bromine: [79.901, 79.907]
    • Thallium: [204.382, 204.385]
  6. Helium does not solidify at a pressure of one atmosphere. Helium can only solidify at pressures above 25 atmospheres, which corresponds to a melting point of 0.95 K.
  7. The atomic weight of commercial lithium can vary between 6.939 and 6.996—analysis of the specific material is necessary to find a more accurate value.
  8. This element sublimes at one atmosphere of pressure.
  9. The element does not have any stable nuclides, and a value in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However, four such elements, bismuth, thorium, protactinium, and uranium, have characteristic terrestrial isotopic compositions, and thus their standard atomic weights are given.
  10. This element is transient – it occurs only through decay (and in the plutonium, also in traces deposited from supernovae onto Earth).
  11. This element is synthetic – the transuranic elements 95 and above do not occur naturally, but they can all be produced artificially.
  12. The value has not been precisely measured, usually because of the element's short half-life; the value given in parentheses is a prediction.
  13. With error bars: 283±11 K and 340±10 K respectively. The best experimental value for the boiling point of copernicium is 357+112
    −108     K.
  14. This predicted value is for solid oganesson, not gaseous oganesson.
  15. With error bars: 350±30 K.
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See also

References
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