Silver sulfide

Silver sulfide
Ball-and-stick model of silver sulfide
Sample of silver sulfide
Names
IUPAC name
Silver(I) sulfide
Other names
Silver sulfide
Argentous 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-blackish crystal
Odor Odorless
Density 7.234 g/cm3 (25 °C)
7.12 g/cm3 (117 °C)
Melting point 836 °C (1,537 °F; 1,109 K)
6.21·10−15 g/L (25 °C)
6.31·10−50
Solubility Soluble in aq. HCN, aq. citric acid with KNO3
Insoluble in acids, alkalies, aqueous ammoniums
Structure
Cubic, cI8 (α-form)
Monoclinic, mP12 (β-form)
Cubic, cF12 (γ-form)
Im3m, No. 229 (α-form)
P21/n, No. 14 (β-form)
Fm3m, No. 225 (γ-form)
2/m (α-form)
4/m 3 2/m (β-form, γ-form)
a = 4.23 Å, b = 6.91 Å, c = 7.87 Å (α-form)
α = 90°, β = 99.583°, γ = 90°
Thermochemistry
76.57 J/mol·K
143.93 J/mol·K
−32.59 kJ/mol
−40.71 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
May cause irritation
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319, H335
P261, P305+P351+P338
NFPA 704 (fire diamond)
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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Infobox references

Silver sulfide is an inorganic compound with the formula Ag
2
S
. A dense black solid, it is the only sulfide of silver. It is useful as a photosensitizer in photography. It constitutes the tarnish that forms over time on silverware and other silver objects. Silver sulfide is insoluble in most solvents, but is degraded by strong acids. Silver sulfide is a network solid made up of silver (electronegativity of 1.98) and sulfur (electronegativity of 2.58) where the bonds have low ionic character (approximately 10%).

Formation

Silver sulfide naturally occurs as the tarnish on silverware. When combined with silver, hydrogen sulfide gas creates a layer of black silver sulfide patina on the silver, protecting the inner silver from further conversion to silver sulfide. Silver whiskers can form when silver sulfide forms on the surface of silver electrical contacts operating in an atmosphere rich in hydrogen sulfide and high humidity. Such atmospheres can exist in sewage treatment and paper mills.

Structure and properties

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. 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. The acanthite, monoclinic, form features two kinds of silver centers, one with two and the other with three near neighbour sulfur atoms. Argentite refers to a cubic form, which, due to instability in "normal" temperatures, is found in form of the pseudomorphosis of acanthite after argentite.

History

In 1833 Michael Faraday noticed that the resistance of silver sulfide decreased dramatically as temperature increased. This constituted the first report of a semiconducting material.

Silver sulfide is a component of classical qualitative inorganic analysis.


This page was last updated at 2024-02-28 05:28 UTC. Update now. View original page.

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