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.

Explanation

(i) All the alkaline earth metals form carbonates `(MCO_(3))`. All these carbonates decompose on heating to given `CO_(2)` and metal oxide. The thermal stability of these carbonates increases down the group i.e., from Be to Ba.
`BeCO_(3) lt MgCO_(3) lt CaCO_(3) lt SCO_(3) lt BaCO_(3)`
`BeCO_(3)` is unstable to the extent that it is stable only in atmosphere of `CO_(2)`. These carbonates however down the group is beryllium oxide i.e., high stable making `BeCO_(3)` 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 (predominatly covalent) all other oxides are ionic and their lattice energy decreases as the size of cation increases.
The oxides are basic nature increases from `BeO` to `BaO` (due to increasing ionic nature)
`ubrace(BeOlt)_("Amphoteric") " "ubrace(MgOlt)_("Weak basic")" "ubrace(CaO lt SrO lt BaO)_("Strong basic")`
BeO dissolves both in acid and alkalies to given 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.