Question

Compare the alkali metals and alkaline earth metals with respect to (a) ionisation enthalpy, (b) basicity of oxides and (c ) solubility of hydroxides.

Answer 1

Alkali metals	Alkaline earth metals
(i) Ionization enthalpy: These have lowest ionization enthalpies in respective periods. This is because of their large atomic sizes. Also, they lose their only valence electron easily as they attain stable noble gas configuration after losing it.	(i) Ionization enthalpy: Alkaline earth metals have smaller atomic size and higher effective nuclear charge as compared to alkali metals. This causes their first ionization enthalpies to be higher than that of alkali metals. However, their second ionization enthalpy is less than the corresponding alkali metals. This is because alkali metals, after losing one electron, acquires noble gas configuration, which is very stable.
(ii) Basicity of oxides: The oxides of alkali metals are very basic in nature. This happens due to the highly electropositive nature of alkali metals, which makes these oxides highly ionic. Hence, they readily dissociate in water to give hydroxide ions.	(ii) Basicity of oxides: The oxides of alkaline earth metals are quite basic but not as basic as those of alkali metals. This is because alkaline earth metals are less electropositive than alkali metals.
(iii) Solubility of hydroxides: The hydroxides of alkali metals are more soluble than those of alkaline earth metals.	(iii) Solubility of hydroxides: The hydroxides of alkaline earth metals are less soluble than those of alkali metals. This is due to the high lattice energies of alkaline earth metals. Their higher charge densities (as compared to alkali metals) account for higher lattice.