Anomalous behavior of first element of every group is due to
1. Small size and high electronegativity
N can form p π – p π multiple bonds whereas P cannot.
2. High IE They form only covalent compounds and not ionic compounds
3. Absence of vacant d orbitals
N cannot form NCl5 or R3N = O since it cannot expand its covalence beyond 4 whereas P can form PCl5 and R3P = O