Write a note on oxidation states of group-15 elements.

Explanation

The common oxidation states of group-15 elements are -3, +3 and +5. The tendency to exhibit -3 oxidation state decrease down the group due to increase in size and metallic character. Infact Bi hardly exists in (-3) oxidation state.
The stability of (+5) oxidation state decreases down the group and that of (+3) oxidation state increases due to inert pair effect. The only compound known of bismuth in (+5) oxidation state is `BiF_(3)`
Nitrogen exhibits (+1), (+2), (+4) oxidation states with oxygen apart from (+5) oxidation state. However, it does not form compounds in (+5) oxidation states with halogens as nitrogen does not have d-orbitals to accomodate electrons from other elements to form bonds.
Nitrogen in all oxidation states from (+1) to (+4) disproportionates in acidic medium. For example :
`underset(+3)(3HNO_(2)) to underset(+5)(HNO_(3)) + H_(2)O + underset(+2)(2NO)`
Phosphorus shows (+1) and (+4) oxidation states in some oxo-acids. Phosphorus disproportionates in all the intermediate states from (-3) to (+5) in acidic or alkaline medium. For example :
`underset(+1)(2H_(3)PO_(2)) overset(Delta)to underset(+5)(H_(3)PO_(4)) + underset(-3)(PH_(3))`
Arsenic, Antimony and Bismuth in (+3) oxidation states are stable with respect to disproportionation.