Why does the reactivity of nitrogen differ from phosphorus ?

Explanation

Nitrogen has a unique ability to form `p pi - p pi ` multiple bonds with itself and with other elements having small size and high electronegativity (e.g. C, O). Therefore, it has triple bond between two nitrogen atoms `(N -= N)` and is non-polar. Due to triple bond it has very high bond enthalpy (941.4 kJ) and therefore, it does not react with other elements under normal conditions and is very unreactive. On the other hand, phosphorus forms single bond (P - P) and is reactive in comparison to nitrogen.