A-Level Trends in the elements across a period and down a group: worked solution

Question

The thermal-stability trend of the Group 2 ethanoates parallels that seen for the Group 2 carbonates. Outline and account for how the thermal stability of the Group 2 ethanoates changes.

Thermal stability of the Group 2 ethanoates increases down the group. Down the group the cationic radius increases, so the charge density (polarising power) of the M2+ ion decreases. The cation therefore polarises/distorts the ethanoate (carboxylate) ion less, weakening it less, so more energy is needed to decompose it. Hence the ethanoates become more thermally stable down the group.