Discuss the anomalous behaviour of nitrogen in group 15 elements. What is the cause of this anomalous behaviour?

Anomalous behaviour of nitrogen:

I)Nitrogen differ from of the members of this group due to its small size, high electronegativity, high ionisation enthalpy and non-availability of d orbitals.

II)Nitrogen has unique ability to form
pπ -pπ multiple bonds with itself and with other elements having small size and high electronegativity (e.g., C, O).

III)Heavier elements of this group do not form pπ -pπ bonds as their atomic orbitals are so large and diffuse that they cannot have effective overlapping.

IV) nitrogen exists as a diatomic molecule with a triple bond (one s and two p) between the two atoms. Consequently, its bond enthalpy
(941.4 kJ mol–1) is very high. On the contrary, phosphorus, arsenic and antimony form single bonds as P–P, As–As and Sb–Sb while
bismuth forms metallic bonds in elemental state. However, the single N–N bond is weaker than the single P–P bond because of high
interelectronic repulsion of the non-bonding electrons, owing to the small bond length. As a result the catenation tendency is weaker in nitrogen.