How does the basicity of oxide of group 2ioncreases down the group?
Answers
The alkali metals and alkaline earth metalsform three different types of binary oxygen compounds: (1) oxides, containing oxide ions, O2−, (2) peroxides, containing peroxide ions, O22−, which contain oxygen-oxygen covalent single bonds, and (3) superoxides, containing superoxide ions, O2−, which also have oxygen-oxygen covalent bonds but with one fewer negative charge than peroxide ions. Alkali metals (which have a +1 oxidation state) form oxides, M2O, peroxides, M2O2, and superoxides, MO2. (M represents a metal atom.) The alkaline earth metals (with a +2 oxidation state) form only oxides, MO, and peroxides, MO2. All the alkali metal oxides can be prepared by heating the corresponding metal nitrate with the elemental metal.2MNO3 + 10M + heat → 6M2O + N2A general preparation of the alkaline earth oxides involves heating the metal carbonates.MCO3 + heat → MO + CO2Both alkali metal oxides and alkaline earth metal oxides are ionic and react with water to form basic solutions of the metal hydroxide.M2O + H2O → 2MOH (where M = group 1 metal)
MO + H2O → M(OH)2 (where M = group 2 metal)Thus, these compounds are often called basic oxides. In accord with their basic behaviour, they react with acids in typical acid-base reactions to produce salts and water; for example,M2O + 2HCl → 2MCl + H2O (where M = group 1 metal).These reactions are also often called neutralization reactions. The most important basic oxides are magnesium oxide (MgO), a good thermal conductor and electrical insulator that is used in firebrick and thermal insulation, and calcium oxide (CaO), also called quicklime or lime, used extensively in the steel industry and in water purification.