Question

Discuss the trend of the following: Thermal stability of carbonates of Group 2 elements.

Answer 1

All the group 2 metals (alkaline earth metals) form carbonates having general formula $MC{O}_3$. They decompose on heating to form $C{O}_2$ and corresponding metal oxides. Thermal stability of the carbonates increases down the group .$BeC{O}_3<MgC{O}_3<CaC{O}_3<SrC{O}_3<BaC{O}_3$.

This stability sequence can be explained in two ways,

a. Size mismatching of cation and anion, as down the group size mismatching decreases, packing efficiency increases. Hence stability of carbonates also increases.

b.$MC{O}_3\to MO+C{O}_2$. Hence more is the stability of metal oxides,lesser will be the stability of the carbonates.$BeO$ is maximum stable, so $BeC{O}_3$ is least stable.