Nitrogen. Ammonia and ammonium salts

The main subgroup of group V holds nitrogen N, phosphorus P, arsenic As, antimony Sb and bismuth Bi; they have 5 outer electrons (ns²np³). By accepting electrons they show –3, by giving them they reach +5. Nitrogen has no d-orbital in its second shell, so its highest valency is IV. In the N₂ molecule two atoms are joined by three shared pairs (N≡N); the bond is nonpolar and very strong, so nitrogen is inert under ordinary conditions. Air contains 78 % nitrogen by volume (about 75.5 % by mass); in compounds it occurs as Chile saltpetre NaNO₃, soil nitrates and proteins. In industry nitrogen is made by slowly evaporating liquid air: nitrogen boils at –196 °C and oxygen at –183 °C, so nitrogen leaves first. It is a colourless, odourless gas, almost insoluble in water. At high temperature (lightning, electric arc) it gives NO with oxygen: N₂ + O₂ ⇌ 2NO – Q; with hydrogen, a catalyst, pressure and heat it gives ammonia: N₂ + 3H₂ ⇌ 2NH₃ + Q. With lithium it reacts under ordinary conditions (6Li + N₂ → 2Li₃N), with magnesium on heating it gives a nitride: 3Mg + N₂ → Mg₃N₂.