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Silver sulfide

Silver sulfide
Ball-and-stick model of silver sulfide
Sample of silver sulfide
Names
IUPAC name
Silver(I) sulfide, Silver sulfide
Identifiers
3D model (Jmol)
ChemSpider
ECHA InfoCard 100.040.384
EC Number 244-438-2
PubChem CID
UNII
Properties
Ag2S
Molar mass 247.80 g·mol−1
Appearance Grayish-black 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
Monoclinic, mP12 (β-form)
Cubic, cI8 (α-form)
Cubic, cF12 (γ-form)
P21/n, No. 14 (α-form)
Im3m, No. 229 (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
Main hazards May cause irritation
GHS pictograms The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Warning
H315, H319, H335
P261, P305+351+338
Irritant Xi
R-phrases R36/37/38
S-phrases S26, S36
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Silver sulfide (Ag
2S) is the sulfide of silver. It is useful as a photosensitizer in photography.

This dense black solid constitutes the tarnish that forms over time on silverware and other silver objects. Silver sulfide is insoluble in all solvents, but is degraded by strong acids. Silver sulfide is an ionic 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. 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.

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. In the acanthite, monoclinic, form there are two crystallographically distinct silver atoms with two and three near neighbour sulfur atoms respectively. 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.


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