Silver sulfide
Encyclopedia
Silver sulfide, Ag2S, is the sulfide
of silver
. 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 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
. When formed on electrical contacts operating in an atmosphere rich in hydrogen sulfide, long filaments known as silver whiskers can form.
are known: monoclinic acanthite
, stable below 500 °C, body centered cubic so-called argentite
, stable above 176 °C, and a high temperature face-centred cubic form stable above 586 °C. The higher temperature forms are electrical conductors. It is found in nature as relatively low temperature mineral acanthite
. 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. Acanthite is an important ore of silver. Ag2S is used as a photosensitizer in photography.
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
of silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
. This dense black solid constitutes the tarnish
Tarnish
Tarnish is a thin layer of corrosion that forms over copper, brass, silver, aluminum, and other similar metals as their outermost layer undergoes a chemical reaction. Tarnish does not always result from the sole effects of oxygen in the air. For example, silver needs hydrogen sulfide to tarnish; it...
that forms over time on silverware and other silver objects. Silver sulfide is insoluble
Solubility
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the used solvent as well as on...
in all solvents, but is degraded by strong acids. Silver sulfide features a covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
, as it is made up of silver (electronegativity
Electronegativity
Electronegativity, symbol χ , is a chemical property that describes the tendency of an atom or a functional group to attract electrons towards itself. An atom's electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the charged nucleus...
of 1.98) and sulfur (electronegativity of 2.58). It is a component of classical qualitative inorganic analysis
Qualitative inorganic analysis
Classical qualitative inorganic analysis is a method of analytical chemistry which seeks to find elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, so that materials in other forms may need to be brought into this state before using standard...
. When formed on electrical contacts operating in an atmosphere rich in hydrogen sulfide, long filaments known as silver whiskers can form.
Structure
Three formsPolymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
are known: monoclinic acanthite
Acanthite
Acanthite, Ag2S, crystallizes in the monoclinic system and is the stable form of silver sulfide below 173 °C. Argentite is the stable form above that temperature. As argentite cools below that temperature its cubic form is distorted to the monoclinic form of acanthite. Below 173 °C...
, stable below 500 °C, body centered cubic so-called argentite
Argentite
Argentite was primarily treated as a mineral belonging to the galena group, cubic silver sulfide , occasionally found as uneven cubes and octahedra, but more often as dendritic or earthy masses, with a blackish lead-grey color and metallic lustre. All these forms are structurally not argentite, but...
, stable above 176 °C, and a high temperature face-centred cubic form stable above 586 °C. The higher temperature forms are electrical conductors. It is found in nature as relatively low temperature mineral acanthite
Acanthite
Acanthite, Ag2S, crystallizes in the monoclinic system and is the stable form of silver sulfide below 173 °C. Argentite is the stable form above that temperature. As argentite cools below that temperature its cubic form is distorted to the monoclinic form of acanthite. Below 173 °C...
. 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. Acanthite is an important ore of silver. Ag2S is used as a photosensitizer in photography.