(i) Ionization enthalpy \(\left(\mathbf{\Delta}_{\mathrm{i}} \mathbf{H}\right)\). Because of higher nuclear charge, the \(\Delta_i H\) of alkaline earth metals are higher than those of the corresponding alkali metals.
(ii) Basicity of oxides. The oxides of alkali and alkaline earth metals dissolve in water to form their respective hydroxides. These hydroxides are strong bases. However, since the ionization enthalpy of alkali metals is lower or the electropositive character of alkali metals is higher than that of the corresponding alkaline earth metal, therefore the \(\mathrm{M}-\mathrm{OH}\) bond in alkali metals can more easily ionize \(\left(\mathrm{MOH} \longrightarrow \mathrm{M}^{+}+\mathrm{OH}^{-}\right)\), than in alkaline earth metals and hence alkali metal oxides are more basic than the corresponding alkaline earth metal oxides.
(iii) Solubility of hydroxides. Because of smaller size and higher ionic charge, the lattice enthalpies of alkaline earth metals are much higher than those of alkali metals and hence the solubility of alkali metal hydroxides is much higher than that of alkaline earth metal hydroxides. However, the solubility of the hydroxides of both alkali and alkaline earth metals increase down the group due to larger decrease in their lattices enthalpies as compared to their hydration enthalpies.