In chemistry, an arsenide is a compound of

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...

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 ...

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 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 properties: they are all ...

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 Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications ...

: :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 zinc blende crystal structure. Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monolithic microwave integrated c ...

(GaAs) features isolated arsenic centers with a zincblende structure ( wurtzite 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 12, by modern IUPAC numbering, is a group of chemical elements in the periodic table. It includes zinc (Zn), cadmium (Cd), mercury (Hg), and copernicium (Cn). Formerly this group was named ''IIB'' (pronounced as "group two B", as the "II" ...

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

graphene Graphene () is an allotrope of carbon consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice nanostructure.

. Cd₃As₂, Zinc arsenide, 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 In solid state chemistry, the fluorite structure refers to a common motif for compounds with the formula MX2. The X ions occupy the eight tetrahedral interstitial sites whereas M ions occupy the regular sites of a face-centered cubic (FCC) structur ...

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 In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. ...

is difficult because these materials are highly covalent and often are best described with

band theory In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy that they may not have (called ''band gaps'' or '' ...

Sperrylite Sperrylite is a platinum arsenide mineral with the chemical formula and is an opaque metallic tin white mineral which crystallizes in the isometric system with the pyrite group structure. It forms cubic, octahedral or pyritohedral crystals in ...

(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 phase In chemistry, a Zintl phase is a product of a reaction between a group 1 (alkali metal) or group 2 ( alkaline earth metal) and main group metal or metalloid (from groups 13, 14, 15, or 16). It is characterized by intermediate metallic/ ionic bond ...

References

Anions Arsenic(−III) compounds {{Inorganic-compound-stub