Hydration Enthalpies

As with the Group 1 ions, hydration enthalpy for the alkaline earth ions falls as ionic size grows down the group:

But because each Group 2 ion carries twice the charge of the corresponding Group 1 ion (for a broadly similar size), their hydration enthalpies are considerably larger across the board than those of the alkali metal ions. This is why alkaline-earth compounds are so often isolated as hydrates where the corresponding alkali metal compound is not: magnesium and calcium chloride crystallise a …