Silver azide

Silver azide is the chemical compound with the formula AgN3. This colorless solid is a well-known explosive.

Silver azide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.034.173
UNII
Properties
AgN3
Molar mass 149.888 g/mol
Appearance colorless solid
Density 4.42 g/cm3, solid
Melting point 250 °C (482 °F; 523 K) explosive
Boiling point decomposes
Solubility in other solvents 2.0×10−8 g/L
Structure
Orthorhombic oI16[1]
Ibam, No 72
Hazards
Main hazards Very toxic, explosive
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 4: Readily capable of detonation or explosive decomposition at normal temperatures and pressures. E.g. nitroglycerinSpecial hazards (white): no code
0
3
4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure and chemistry

Silver azide can be prepared by treating an aqueous solution of silver nitrate with sodium azide.[2] The silver azide precipitates as a white solid, leaving sodium nitrate in solution.

AgNO
3 (aq) + NaN
3 (aq) → AgN
3 (s) + NaNO
3 (aq)

X-ray crystallography shows that AgN3 is a coordination polymer with square planar Ag+ coordinated by four azide ligands. Correspondingly, each end of each azide ligand is connected to a pair of Ag+ centers. The structure consists of two-dimensional AgN3 layers stacked one on top of the other, with weaker Ag–N bonds between layers. The coordination of Ag+ can alternatively be described as highly distorted 4 + 2 octahedral, the two more distant nitrogen atoms being part of the layers above and below.[3]

Part of a layer
Layer stacking
4 + 2 coordination of Ag+
2 + 1 coordination of N in N−
3

In its most characteristic reaction, the solid decomposes explosively, releasing nitrogen gas:

2 AgN
3 (s) → 3 N
2 (g) + 2 Ag (s)

The first step in this decomposition is the production of free electrons and azide radicals; thus the reaction rate is increased by the addition of semiconducting oxides.[4] Pure silver azide explodes at 340 °C, but the presence of impurities lowers this down to 270 °C.[5] This reaction has a lower activation energy and initial delay than the corresponding decomposition of lead azide.[6]

Safety

AgN3, like most heavy metal azides, is a dangerous primary explosive. Decomposition can be triggered by exposure to ultraviolet light or by impact.[2] Ceric ammonium nitrate is used as an oxidising agent to destroy AgN
3 in spills.[5]

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See also

References
  1. Marr H.E. III.; Stanford R.H. Jr. (1962). "The unit-cell dimensions of silver azide". Acta Crystallographica. 15 (12): 1313–1314. doi:10.1107/S0365110X62003497.
  2. Robert Matyas, Jiri Pachman (2013). Primary Explosives (1st ed.). Springer. p. 93. ISBN 978-3-642-28435-9.
  3. Schmidt, C. L. Dinnebier, R.; Wedig, U.; Jansen, M. (2007). "Crystal Structure and Chemical Bonding of the High-Temperature Phase of AgN3". Inorganic Chemistry. 46 (3): 907–916. doi:10.1021/ic061963n. PMID 17257034.CS1 maint: multiple names: authors list (link)
  4. Andrew Knox Galwey; Michael E. Brown (1999). Thermal decomposition of ionic solids (vol.86 of Studies in physical and theoretical chemistry. Elsevier. p. 335. ISBN 978-0-444-82437-0.
  5. Margaret-Ann Armour (2003). Hazardous laboratory chemicals disposal guide, Environmental Chemistry and Toxicology (3rd ed.). CRC Press. p. 452. ISBN 978-1-56670-567-7.
  6. Jehuda Yinon; Shmuel Zitrin (1996). Modern Methods and Applications in Analysis of Explosives. John Wiley and Sons. pp. 15–16. ISBN 978-0-471-96562-6.
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