Question

Compare the alkali metals and alkaline earth metals with respect to (i) ionisation enthalpy (ii) basicity of oxides and (iii) solubility of hydroxides.

Answer 1

(i) Ionization enthalpy:
Alkaline earths have higher ionization enthalpy values than alkali metals. This is because the atomic size of alkaline earths is smaller than that of alkali metals.
(ii) Basicity of oxides:
On dissolution in water, the oxides of alkali metals and alkaline earth metals form basic hydroxides. The basicity of alkali metal oxides is higher than that of alkaline earth metal oxides due to lower ionization enthalpy of alkali metals than that of corresponding alkaline earths. Due to this, the M-OH bond in alkali metal hydroxides can more easily ionize.
(iii) Solubility of hydroxides:
Alkaline earths have larger lattice energies than alkali metals due to small size and high charge. Hence, alkaline earth metal hydroxides have lower solubility than alkali metals.