p-block Elements | Nitrogen Family Elements, IIT JEE & NEET

The order of basic character is NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃. Basic character depends on the availability of the lone pair on the central atom. As atomic size increases down the group, the electron density on the central atom decreases (lone pair is more diffuse), making it less effective at donating to a proton or Lewis acid.

Nitrogen cannot form pentahalides because it lacks d-orbitals in its valence shell (second period, n=2). Expanding the octet beyond 4 bonds requires empty d-orbitals for hybridisation (sp³d). Phosphorus, belonging to the third period, has available 3d orbitals and can form PCl₅. This is one of the most frequently tested concepts in JEE Main inorganic chemistry.

Group 15 (Nitrogen Family) elements have the general valence shell electronic configuration ns²np³. The three half-filled p-orbitals give these elements extra stability. This configuration is shared by N, P, As, Sb, and Bi. The half-filled stability explains why nitrogen has a higher ionisation enthalpy than oxygen, despite oxygen being more electronegative overall

Nitrogen gas is prepared in the laboratory by the thermal decomposition of ammonium dichromate or by heating an aqueous solution of ammonium nitrite (NH₄NO₂):NH₄NO₂ → N₂ + 2H₂O (on gentle heating)Industrially, nitrogen is obtained by the fractional distillation of liquid air. The N₂ produced is very pure and used in the Haber Process for ammonia synthesis.

Phosphorus has three main allotropes: white phosphorus (P₄, tetrahedral, highly reactive, toxic, stored under water), red phosphorus (polymeric chain structure, less reactive, non-toxic), and black phosphorus (layered structure, most stable, least reactive). White phosphorus is used in matches and incendiary devices. NEET frequently tests the differences in reactivity and structure between white and red phosphorus

NH₃ has a significantly higher boiling point (−33°C) than PH₃ (−88°C) despite PH₃ having a higher molecular mass. This is because NH₃ molecules form intermolecular hydrogen bonds due to the high electronegativity and small size of nitrogen. Phosphorus is not electronegative enough to form hydrogen bonds, so PH₃ is held together only by weak van der Waals forces.