oxyanion

An oxyanion, or oxoanion, is an ion with the generic formula (where 'A' represents a chemical element and 'O' represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The corresponding oxyacid of an oxyanion is the compound . The structures of condensed oxyanions can be rationalized in terms of AO polyhedral units with sharing of corners or edges between polyhedra. The oxyanions (specifically, phosphate and polyphosphate esters) adenosine monophosphate (AMP), adenosine diphosphate (ADP) and adenosine triphosphate (ATP) are important in biology.

==Monomeric oxyanions== The formula of monomeric oxyanions, , is dictated by the oxidation state of the element 'A' and its position in the periodic table. Elements of the first row are limited to a maximum coordination number of 4. However, none of the first row elements has a monomeric oxyanion with that coordination number. Instead, carbonate () and nitrate () have a trigonal planar structure with π bonding between the central atom and the oxygen atoms. This π bonding is favoured by the similarity in size of the central atom and oxygen.