Names | |
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IUPAC name
Silver(I) sulfide
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Other names
Silver sulfide
Argentous sulfide | |
Identifiers | |
3D model (JSmol)
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ChemSpider | |
EC Number |
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PubChem CID
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Properties | |
Ag2S | |
Molar mass | 247.80 g·mol−1 |
Appearance | Grayish-blackish 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 (25 °C) | |
Solubility product (Ksp)
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6.31·10−50 |
Solubility | Soluble in aq. HCN, aq. citric acid with KNO3 Insoluble in acids, alkalies, aqueous ammoniums[4] |
Structure | |
Cubic, cI8 (α-form) Monoclinic, mP12 (β-form) Cubic, cF12 (γ-form)[3][5] | |
Im3m, No. 229 (α-form)[5] P21/n, No. 14 (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°
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Thermochemistry | |
Heat capacity (C)
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76.57 J/mol·K[6] |
Std molar
entropy (S |
143.93 J/mol·K[6] |
Std enthalpy of
formation (ΔfH⦵298) |
−32.59 kJ/mol[6] |
Gibbs free energy (ΔfG˚)
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−40.71 kJ/mol[6] |
Hazards | |
Main hazards | May cause irritation |
GHS pictograms | [2] |
GHS Signal word | Warning |
H315, H319, H335[2] | |
P261, P305+351+338[2] | |
NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
verify (what is ?) | |
Infobox references | |
Silver sulfide is an inorganic compound with the formula Ag2S. 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%).
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.[8] 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.[9] Such atmospheres can exist in sewage treatment and paper mills.[10][11]
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. The acanthite, monoclinic, form features two kinds of silver centers, one with two and the other with three near neighbour sulfur atoms.[12] Argentite refers to a cubic form, which, due to instability in "normal" temperatures, is found in form of the pseudomorphosis of acanthite after argentite.
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.[13]
Silver sulfide is a component of classical qualitative inorganic analysis.[14]
Original source: https://en.wikipedia.org/wiki/Silver sulfide.
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