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Silver sulfide

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Silver sulfide
Ball-and-stick model of silver sulfide
Sample of silver sulfide
Names
IUPAC name
Silver(I) sulfide, Silver sulfide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.040.384 Edit this at Wikidata
EC Number
  • 244-438-2
UNII
  • InChI=1S/2Ag.S/q2*+1;-2 ☒N
    Key: XUARKZBEFFVFRG-UHFFFAOYSA-N ☒N
  • [S-2].[Ag+].[Ag+]
Properties
Ag2S
Molar mass 247.80 g·mol−1
Appearance Grayish-black crystal
Odor Odorless
Density 7.234 g/cm3 (25 °C)[1][2]
7.12 g/cm3 (117 °C)[3]
Melting point 836 °C (1,537 °F; 1,109 K)[1]
6.21·10−15 g/L (20 °C)
6.31·10−50
Solubility Soluble in aq. HCN, aq. citric acid with KNO3
Insoluble in acids, alkalies, aqueous ammoniums[4]
Structure
Monoclinic, mP12 (β-form)
Cubic, cI8 (α-form)
Cubic, cF12 (γ-form)[3][5]
P21/n, No. 14 (α-form)[5]
Im3m, No. 229 (β-form)
Fm3m, No. 225 (γ-form)[3]
2/m (α-form)[5]
4/m 3 2/m (β-form, γ-form)[3]
a = 4.23 Å, b = 6.91 Å, c = 7.87 Å (α-form)[5]
α = 90°, β = 99.583°, γ = 90°
Thermochemistry
76.57 J/mol·K[6]
143.93 J/mol·K[6]
−32.59 kJ/mol[6]
−40.71 kJ/mol[6]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 May cause irritation
GHS labelling:
GHS07: Exclamation mark[2]
Warning
H315, H319, H335[2]
P261, P305+P351+P338[2]
NFPA 704 (fire diamond)
[7]
NFPA 704 four-colored diamondHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
0
0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Silver sulfide (Ag
2S) is the sulfide of silver. It is useful as a photosensitizer in photography.

Properties

This dense black solid constitutes the tarnish that forms over time on silverware and other silver objects.[8] Silver sulfide is insoluble in all solvents, but is degraded by strong acids. Silver sulfide features a covalent bond, as it is made up of silver (electronegativity of 1.98) and sulfur (electronegativity of 2.58). It is a component of classical qualitative inorganic analysis.[9] When formed on electrical contacts operating in an atmosphere rich in hydrogen sulfide, long filaments known as silver whiskers can form.

Degrading wooden treasure chests aboard sunken galleons can provide the sulfide needed for certain sulfide ion consuming bacteria to produce hydrogen sulfide gas. When combined with silver the hydrogen sulfide gas creates a layer of black silver sulfide patina on the silver, protecting the inner silver from further conversion to silver sulfide. [10]

Structure

Three forms are known: monoclinic acanthite (β-form), stable below 179 °C, body centered cubic so-called argentite (α-form), stable above 180 °C, and a high temperature face-centred cubic (γ-form) stable above 586 °C.[5] The higher temperature forms are electrical conductors. It is found in nature as relatively low temperature mineral acanthite. Acanthite is an important ore of silver. In the acanthite, monoclinic, form there are two crystallographically distinct silver atoms with two and three near neighbour sulfur atoms respectively.[11] The name argentite refers to a cubic form, which, due to instability in "normal" temperatures, is found in form of the pseudomorphosis of acanthite after argentite.

References

  1. ^ a b Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0.
  2. ^ a b c d Sigma-Aldrich Co., Silver sulfide. Retrieved on 2014-07-13.
  3. ^ a b c d Tonkov, E. Yu (1992). High Pressure Phase Transformations: A Handbook. Vol. 1. Gordon and Breach Science Publishers. p. 13. ISBN 2-88124-761-X.
  4. ^ Comey, Arthur Messinger; Hahn, Dorothy A. (February 1921). A Dictionary of Chemical Solubilities: Inorganic (2nd ed.). New York: The MacMillan Company. p. 835.
  5. ^ a b c d e "Silver sulfide (Ag2S) crystal structure". 41C. Springer Berlin Heidelberg. 1998: 1–4. doi:10.1007/10681727_86. ISBN 978-3-540-31360-1. {{cite journal}}: Cite journal requires |journal= (help)
  6. ^ a b c d Pradyot, Patnaik (2003). Handbook of Inorganic Chemicals. The McGraw-Hill Companies, Inc. p. 845. ISBN 0-07-049439-8.
  7. ^ "MSDS of Silver Sulfide". saltlakemetals.com. Utah, USA: Salt Lake Metals. Retrieved 2014-07-13.
  8. ^ "Silver". chemistryexplained.com. Advameg, Inc. Retrieved 2014-07-13.
  9. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
  10. ^ Zumdahl, Steven S.; DeCoste, Donald J. (2013). Chemical Principles (7th ed.). p. 505. ISBN 978-1-111-58065-0.
  11. ^ FRUEH, A. J. (1958). The crystallography of silver sulfide, Ag2S. Zeitschrift für Kristallographie-Crystalline Materials, 110(1-6), 136-144.

Tarnishing of Silver: A Short Review V&A Conservation Journal

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