Dioxides (oxidation state +4) Structure a) CO2 - molecular b) SiO2 - macromolecular c) GeO2, SnO2, PbO2 - intermediate between ionic and macomolecular Acidity a) CO2 and SiO2 are acid and react with alkalis to form salts. CO2(g) + 2NaOH(aq) → Na2CO3(aq) + H2O(l) b) GeO, SnO2 and PbO2 are amphoteric and will react with both acids and alkalis. SnO2(s) + conc. HCl(l) → SnCl4(l) + 2H2O(l) SnO2(s) + 2OH-(aq) → SnO32-(aq) + H2O(l) Thermal stability They are very stable to high temperature except PbO2 which readily loses O2. 2PbO2(s) → 2PbO(s) + O2(g) Monoxides (Oxidation State +2) Structure a) CO and SiO are molecular. CO has a lone pair of electrons hence, can act as a ligand forming complexes with transition metals. For example: Ni(CO)42+ b) GeO, SnO, PbO are mainly ionic. Acidity a) CO and SiO are neutral and react neither with acids or alkalis. b) GeO, SnO, PbO are amphoteric. SnO(s) + 2HCl(aq) → SnCl2(aq) + H2O(l)SnO(s) + 2OH-(aq) → [Sn(H204)4]2-(aq) Thermal stability The only stable one is PbO. The others are readily oxidised on standing in air to the dioxide.