• # question_answer 11) Compare the alkali metals and alkaline earth metals with respect to (i) ionisation enthalpy (ii) basicity of oxides (iii) solubility of hydroxides.

(i) Ionisation enthalpy: On account of higher nuclear charge and smaller radii, the first ionization enthalpies of alkaline earth metals are higher than those of corresponding alkali metals. However, second ionisation enthalpies of alkaline earth metals are lower than those of corresponding alkali metals as alkali metals ions $({{M}^{+}})$ have inert gas configurations. (ii) Basicity of oxides: The oxides of both alkali and alkaline earth metals are basic in nature. They combine with water and form strong bases. However, the hydroxides of alkali metals easily ionise to furnish $O{{H}^{-}}$ions as their ionization enthalpies are lower than alkaline earth metals. Hence, the oxides of alkali metals are more basic than the corresponding alkaline earth metal oxides. (iii) Solubility of hydroxides: On account of smaller size and higher charge on the ions of alkaline earth metals, the lattice energies of the hydroxides of alkaline earth metals are much higher than those of the alkali metal hydroxides. Hence, the solubility of hydroxides of alkaline earth metals is lower than corresponding hydroxides of alkali metals. However, solubility increases in both the groups from top to bottom.