JEE Main · 2025 · 22 Jan 2025 · Shift 2 · p-Block Elements

Group 15 contains N, P, As, Sb, Bi, and single E–E bond strength runs N–N < P–P < As–As < Sb–Sb: nitrogen's very small atomic size crowds the lone pairs on the two bonded nitrogen atoms close together, and the resulting lone pair–lone pair repulsion weakens the N–N bond far more than the analogous repulsion in the larger P–P, As–As, or Sb–Sb bonds. So the element E with the weakest E–E bond is nitrogen.

Nitrogen's ground-state configuration is $1s^{2}2s^{2}2p^3$, with no accessible d-orbitals, so it cannot expand its octet by promoting electrons the way phosphorus or arsenic can. Its normal covalency from the three unpaired 2p electrons is 3, but nitrogen can also donate its 2s lone pair into an empty orbital of a suitable acceptor to form one coordinate bond, as it does in $\mathrm{N}{\mathrm{H}}_4^{+}$ and ${\mathrm{N}}_2\mathrm{O}$.

Adding this dative bond to the three normal covalent bonds gives nitrogen a maximum covalency of 4.