Nitrogen has a unique ability to form pπ – pπ multiple bonds withitself and with other elements having small size and high electronegativity.Consequently, its bond enthalpy is very high and reactivity is less.Another factor which affects the chemistry of N is the absence ofd-orbitals in its valence shell. As a result, not only the covalency ofN is restricted to four, it can also not form dπ – pπ bonds. P on the otherhand, does not form pπ – pπ bonds and hence it only forms a P – P singlebond, which can easily be broken. Also, phosphorus has vacant d-orbitalsand can form dπ – dπ bond with transition metals to form compoundswhich can act as ligands.