Reactivity towards air/oxygen

Reactivity towards air or oxygen follows a distinct pattern in each group. Group 13 elements, on heating in air or oxygen, form an oxide of type E2O3 (4E(s) + 3O2(g), heated, → 2E2O3(s)) and can likewise form a nitride EN on heating with nitrogen (2E(s) + N2(g), heated, → 2EN(s)). Group 14 elements form either EO or EO2 depending on the stable oxidation state of the element and how much oxygen is available (E(s) + ½O2(g), heated, → EO; E(s) + O2(g), heated, → EO2). Group 15 elements form two types of oxide, E2O3 and E2O5 — for example P4 + 3O2 → P4O6, while P4 + 5O2 → P4O10; arsenic similarly gives As4O6, and bismuth (which favours its lower, +3 oxidation state because of the inert-pair effect) gives only Bi2O3, from 2Bi + 3O2 → Bi2O3. Across all three groups, increasing metallic character down the group is reflected in the nature of these oxides, which change gradually from acidic, through amphoteric, to basic — see Table 9.6 for the complete set: boron's B2O3 is acidic, aluminium's and gallium's oxides are amphoteric, and indium's and thallium's oxides are basic; the same acidic-t …