Q.Write the valence shell electronic configuration of group-15 elements.

Group 15 (the pnictogens/nitrogen family) consists of nitrogen, phosphorus, arsenic, antimony and bismuth, all sharing the outer configuration ns2 np3. Nitrogen, about 78% of the atmosphere by volume, also occurs combined as Chile saltpetre (NaNO3) and Indian saltpetre (KNO3). Phosphorus, the 11th most abundant crustal element, is never free, occurring instead as fluorapatite, chlorapatite and hydroxyapatite. Arsenic, antimony and bismuth are comparatively scarce and occur mainly as sulphide ores.

Down the group, atomic radius, atomic mass and (generally) melting/boiling point rise, while nitrogen alone is a gas and the rest are solids; density rises sharply from nitrogen's near-negligible gas density to bismuth's 9.79 g/cm3. Nitrogen's exceptionally stable half-filled 2p3 configuration gives it a high first ionisation enthalpy and the third-highest electronegativity of any element, and, combined with its small size and lack of accessible d orbitals, this makes nitrogen chemically anomalous within its own group: it strongly prefers pπ-pπ multiple bonding with itself (N≡N) and cannot expand its octet the way phosphorus and heavier members can (which instead favour catenated single bonds, as in P4, and readily form 5-coordinate species like PCl5). This same small size/high electronegativity/no-d-orbitals trio also underlies the classic "inert pair effect" seen most strongly at the bottom of the group: bismut …