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In chemistry, an arsenide is a compound of arsenic with a less electronegative 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, borides, silicides and nitrides.
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Alkali metal and alkaline earth arsenides
The group 1 alkali metals and the group 2, alkaline earth metals, 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 NaOHTransition metal arsenides
A number of arsenide minerals are known, for example nickeline, NiAs, skutterudite, CoAs3 (a diamagnetic semiconductor) Assigning formal oxidation numbers (states) is difficult unless the structure is known, for example the mineral sperrylite (PtAs2), platinum arsenide, has a formal oxidation state for arsenic of –2. as the solid is usually described as Pt4+,As24−.
The arsenides of the transition metals are mainly of interest because they represent or 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 a poisonous and mobile.
III-V Compounds
Many arsenides of the group III elements are valuable semiconductors. Gallium arsenide (GaAs) features isolated arsenic centers with a zincblende structure (wurtzite structure can eventually also form in nanostructures), and with predominantly covalent bonding - it is III–V semiconductor.