Oxyanion

An oxyanion is a polyatomic ion that contains oxygen atoms bonded to a central nonmetal element. Oxyanions arise when oxyacids lose one or more protons, producing the conjugate base. The negative charge is delocalized over the oxygen atoms by resonance, giving each oxyanion characteristic stability.

Naming and patterns: In many chemical families, the same central element has several oxyanions that differ in the number of oxygens. The -ate suffix denotes the more highly oxygenated form, while -ite denotes one fewer oxygen. Prefixes hypo- and per- indicate two fewer or one more oxygen than the -ite/-ate form, respectively. Common examples include nitrate NO3-, nitrite NO2-, sulfate SO4 2-, sulfite SO3 2-, carbonate CO3 2-, bicarbonate HCO3-, phosphate PO4 3-, hydrogen phosphate HPO4 2-, chlorate ClO3-, perchlorate ClO4-, hypochlorite ClO−, chlorite ClO2-.

Structure and chemistry: The central atom is typically a nonmetal such as nitrogen, sulfur, phosphorus, chlorine, carbon, or halogens. The overall charge is distributed over the oxygen atoms, and the oxyanion is usually the conjugate base of an oxyacid HXO_y. In aqueous solution these species participate in acid–base equilibria and redox processes, and their stability is influenced by resonance, electronegativity, and the number of surrounding oxygens.

Importance: Oxyanions are central in environmental and biological systems. Nitrate and nitrite are key in the nitrogen cycle and water quality; sulfate and sulfite play roles in mineralogy and respiration; carbonate and phosphate are essential in buffering, geology, and biochemistry.