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Arsenic is used as the group 15 element in the III-V semiconductors gallium arsenide, indium arsenide, and aluminium arsenide. [10] The valence electron count of GaAs is the same as a pair of Si atoms, but the band structure is completely different which results in distinct bulk properties. [11]
The arsenate is an ion with the chemical formula AsO 3− 4. [1] Bonding in arsenate consists of a central arsenic atom, with oxidation state +5, double bonded to one oxygen atom and single bonded to a further three oxygen atoms. [2] The four oxygen atoms orient around the arsenic atom in a tetrahedral geometry. [2]
Arsenic (III) binding sites usually use thiol groups of cysteine residues. The catalysis involves thiolates of Cys72, Cys174, and Cys224. In an SN2 reaction, the positive charge on the SAM sulfur atom pulls the bonding electron from the carbon of the methyl group, which interacts with the arsenic lone pair to form an As−C bond, leaving SAH. [31]
Arsenic also bonds readily to itself as seen in the square As 3− 4 ions in the mineral skutterudite. [33] In the +3 oxidation state , arsenic is typically pyramidal owing to the influence of the lone pair of electrons .
In all of these the geometry around the As III centers are approximately trigonal, the lone pair on the arsenic atom is stereochemically active. [1] Well known examples of arsenites include sodium meta-arsenite which contains a polymeric linear anion, (AsO − 2) n, and silver ortho-arsenite, Ag 3 AsO 3, which contains the trigonal AsO 3− 3 ...
Similarly, realgar has arsenic–arsenic bonds, so the arsenic's oxidation state is +II. A corresponding compound for antimony is Sb 2 (C 6 H 5) 4, where the antimony's oxidation state is +II. Phosphorus has the +1 oxidation state in hypophosphorous acid and the +4 oxidation state in hypophosphoric acid.
The two unique forms of potassium arsenite can be attributed to the different number of oxygen atoms. Potassium meta-arsenite (KAsO 2) contains two oxygen atoms one of which is bonded to the arsenic atom via a double bond. Conversely, Potassium ortho-arsenite (K 3 AsO 3) consists of three oxygen atoms all bound to the arsenic atom via single bonds.
Arsenic-arsenic bonds are very weak, and oligomeric arsenic compounds are even more liable to oxidize than their hydrogenated precursors. [6]: 318–320 The following reaction can, however, be prepared through electrochemical reduction in a zinc-sulfate cell. [6]: 473 Oxidation first forms polymeric arsinoxides, e.g.: MeAs + O → MeAsO