In the form of elemental nitrogen it exists as a diatomic molecule (N 2 ). This is due to the fact that nitrogen can form p π -p π multiple bond (N ≡ N) because of small size of nitrogen atom. Heavier elements of this group do not able to form p π -p π bonds as their atomic orbitals are so large and diffuse that they cannot have effective overlapping. Further P – P single bond is stronger than N – N single bond. Hence phosphorus as tendency to under go catenation.

N ≡ N (N 2 ) (P 4 )