34. Discuss the trend of the following

(i) Thermal stability of carbonates of Group 2 elements.

(ii) The solubility and the nature of oxides of Group 2 elements.

(i) All the alkaline earth metals from carbonates $\left({\mathrm{MCO}}_{3}\right)$. All these carbonates decompose on heating to give CO2 and metal oxide. The thermal stability of these carbonates increases down the group i.e., from Be to Ba.
${\mathrm{BeCO}}_{3}<{\mathrm{MgCO}}_{3}<{\mathrm{CaCO}}_{3}<{\mathrm{SCO}}_{3}<{\mathrm{BaCO}}_{3}$
BeCO3 is unstable to the extent that it is stable only in atmosphere of CO2. These carbonates however show reversible decomposition in closed container.
${\mathrm{BeCO}}_{3}⇌\mathrm{BeO}+{\mathrm{CO}}_{2}$
Hence, more is the stability of oxide formed, less will be stability of carbonates. Stability of oxides decreases down the group is beryllium oxide i.e., high stable making BeCO3 unstable.
(ii) All the alkaline earth metals form oxides of formula MO. The oxides are very stable due to high lattice energy and are used as refractory material.
Except BeO (perdominantly covalent) all other oxides are ionic and their lattice energy decreases as the size of cation increases.
The oxides are basic and basic nature increases from BeO to BaO (due to increasing ionic nature).
BeO dissolves both in acid and alkalies to give salts and is amphoteric
The oxides of the alkaline earth metals (except BeO and MgO) dissolve in water to form basic hydroxides and evolve a large amount of heat. BeO and MgO possess high lattice energy and thus insoluble in water.