Final answer:
The solubility of group 2 hydroxides and sulfates changes down the group due to differences in ionic size, lattice energy, and the ability to form complex ions. Hydroxides become more soluble as ionic size increases, while the solubility of sulfates decreases due to less effective polarization.
Step-by-step explanation:
The solubility of group 2 hydroxides increases down the group, while for group 2 sulfates, it decreases. This can be attributed to the varying solubility rules and the differing reactions these compounds have with water.
For hydroxides, increasing atomic radius and decreasing electronegativity as you move down group 2 result in weaker forces holding the ions together, which makes them more soluble. With sulfates, the larger cations of heavier group 2 elements polarize the sulfate ion less effectively, leading to lower solubility. Moreover, the solubility may also depend on the formation of complex ions and the ability of anions to react with water to enhance solubility.
The general trend is such that hydroxides become more soluble due to the larger ionic size of the metal ions causing weaker ionic attraction within the lattice, making lattice energies decrease more rapidly than hydration energies do. This is not the same for sulfates, where the decrease in lattice energy does not overcome the decrease in hydration energy, leading to reduced solubility.