The size of `CO_(3)^(2-)` and `SO_(4)^(-)` ions are much bigger than those of the cations . Therefore , the lattice enthalpies of carbonates and sulphates remain almost the same as we move down the group . Since the hydration enthalpies decrease as the size of the cation increases down the group , the solubility of carbonates and sulphates of alkaline earth metals decreases down the group .
