27.1 Trends in Group 2 metals and compounds

Heating Group 2 nitrates and carbonates gives an oxide plus gaseous products. Thermal stability generally increases down the group as larger M²⁺ ions polarise the large anions less strongly.

A small, high-charge-density cation distorts carbonate or nitrate electron density, weakening the anion and making decomposition easier. Compare ionic radius and charge rather than memorising isolated temperatures.

MgCO₃ decomposes more readily than BaCO₃. The trend applies to both anions but the actual decomposition temperatures differ.

Do not explain stability by saying “all bonds get stronger down the group”; the key is cation polarisation of the anion.

Dissolution is favoured when hydration enthalpy gained offsets lattice energy required. Group 2 hydroxide and sulfate trends differ because lattice and hydration terms change at different rates down the group.

Use the energy balance and the measured solubility together; a more exothermic solution enthalpy does not automatically mean greater solubility because entropy also contributes.

Hydroxide solubility generally rises down Group 2 while sulfate solubility falls, showing that one simple “larger ion” rule cannot explain both salts.

Do not equate ΔHsol directly with solubility or ignore the opposing lattice/hydration terms.