The chemistry of arsenic is predominately nonmetallic. Whether or not arsenic forms a cation is unclear. Its many metal alloys are mostly brittle. It shows fewer tendencies to anionic behaviour than ordinary nonmetals. Its solution chemistry is characterised by the formation of oxyanions. Arsenic generally forms compounds in which it has an oxidation state of +3 or +5. The halides, and the oxides and their derivatives are illustrative examples. In the trivalent state, arsenic shows some incipient metallic properties. The halides are hydrolysed by water but these reactions, particularly those of the chloride, are reversible with the addition of a hydrohalic acid. The oxide is acidic but, as noted below, (weakly) amphoteric. The higher, less stable, pentavalent state has strongly acidic (nonmetallic) properties. Compared to phosphorus, the stronger metallic character of arsenic is indicated by the formation of oxoacid salts such as AsPO 4, As 2 (SO 4) 3 and arsenic acetate As(CH 3 COO) 3. The oxide As 2 O 3 is polymeric, amphoteric, and a glass former. Arsenic has an extensive organometallic chemistry (see Organoarsenic chemistry).