In chemistry, an arsenide is a compound of

arsenic Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...

with a less

electronegative Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...

element or elements. Many metals form binary compounds containing arsenic, and these are called arsenides. They exist with many stoichiometries, and in this respect arsenides are similar to phosphides.

Alkali metal and alkaline earth arsenides

The group 1

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

s and the group 2,

alkaline earth metal The alkaline earth metals are six chemical elements in group (periodic table), group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar p ...

s, form arsenides with isolated arsenic atoms. They form upon heating arsenic powder with excess sodium gives sodium arsenide (Na₃As). The structure of Na₃As is complex with unusually short Na–Na distances of 328–330 pm which are shorter than in sodium metal. This short distance indicates the complex bonding in these simple phases, i.e. they are not simply salts of As³⁻ anion, for example. The compound LiAs, has a metallic lustre and electrical conductivity indicating some metallic bonding. These compounds are mainly of academic interest. For example, "sodium arsenide" is a structural motif adopted by many compounds with the A₃B stoichiometry. Indicative of their salt-like properties, hydrolysis of alkali metal arsenides gives arsine: :Na₃As + 3 H₂O → AsH₃ + 3 NaOH

III–V compounds

Many arsenides of the group 13 elements (group III) are valuable semiconductors.

Gallium arsenide Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a Zincblende (crystal structure), zinc blende crystal structure. Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monoli ...

(GaAs) features isolated arsenic centers with a

zincblende Sphalerite is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in sedimentary exhalative, Mississippi-Valley type, and volcanogenic mas ...

structure (

wurtzite Wurtzite is a zinc and iron sulfide mineral with the chemical formula , a less frequently encountered Polymorphism (materials science), structural polymorph form of sphalerite. The iron content is variable up to eight percent.Palache, Charles, H ...

structure can eventually also form in nanostructures), and with predominantly covalent bonding – it is a III–V semiconductor.

II–V compounds

Arsenides of the group 12 elements (group II) are also noteworthy. Cadmium arsenide (Cd₃As₂) was shown to be a three-dimensional (3D) topological Dirac semimetal analogous to

graphene Graphene () is a carbon allotrope consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice, honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating ...

. Cd₃As₂, Zn₃As₂ and other compounds of the Zn-Cd-P-As quaternary system have very similar crystalline structures, which can be considered distorted mixtures of the zincblende and antifluorite crystalline structures.

Polyarsenides

Transition metal arsenides

Arsenic anionics are known to catenate, that is, form chains, rings, and cages. The mineral skutterudite (CoAs₃) features rings that are usually described as . Assigning formal oxidation numbers is difficult because these materials are highly covalent and often are best described with band theory. Sperrylite (PtAs₂) is usually described as . The arsenides of the transition metals are mainly of interest because they contaminate sulfidic ores of commercial interest. The extraction of the metals – nickel, iron, cobalt, copper – entails chemical processes such as smelting that poses environmental risks. In the mineral, arsenic is immobile and poses no environmental risk. Released from the mineral, arsenic is poisonous and mobile.

Zintl phases

Partial reduction of arsenic with alkali metals (and related electropositive elements) affords polyarsenic compounds, which are members of the Zintl phases.

References

{{Monatomic anion compounds Anions Arsenic(−III) compounds