Chapter 15: The Group 15 Elements

Nitrogen's fundamental role stems from its highly stable diatomic molecule with a strong triple bond, while phosphorus manifests in multiple allotropic forms including white, red, and black varieties with distinct structural arrangements based on tetrahedral or layered frameworks. The heavier members of the group transition toward metallic character with layered hexagonal solid structures, though they maintain important semiconductor and chemical properties. The inert-pair effect becomes increasingly significant moving down the group, stabilizing lower oxidation states such as the +3 state in bismuth compounds while lighter elements access higher oxidation states including +5. Binary compounds derived from Group 15 elements include diverse nitride classifications ranging from ionic to covalent to interstitial types, alongside azide species that serve as explosives and coordination ligands. Phosphide, arsenide, antimonide, and bismuthide compounds exhibit technological importance particularly in semiconductor manufacturing. Hydride chemistry encompasses ammonia, hydrazine, hydroxylamine, and the corresponding heavier hydrides, which find use as fertilizers, rocket propellants, and ligands in coordination complexes. Halide and oxohalide species demonstrate pronounced periodic trends, from the inherent instability of nitrogen trihalides to the thermodynamic stability of pentahalides formed by heavier congeners, with applications extending to superacid synthesis. Oxide chemistry and oxoanion formation vary considerably across the group, from simple nitrogen oxides to polymeric phosphorus oxides and their corresponding oxoanions, all bearing significance for biological function, fertilizer production, and environmental processes. The chapter covers extraction and processing methods for each element and their major industrial applications spanning fertilizer production, explosives manufacture, semiconductor technology, alloy formation, and pharmaceutical development. Particular emphasis is given to nitrogen fixation, contrasting the energy-intensive Haber-Bosch industrial synthesis with the enzymatic mechanisms of biological nitrogenase containing iron and molybdenum cofactors. Advanced topics include condensed phosphate structures, phosphazene polymers with potential biomedical applications, and organoarsenic compounds alongside associated environmental and toxicological concerns.