The solubilities of carbonates decrease down the magnesium...

The solubilities of carbonates decrease down the magnesium group due to a decrease in [2003]
(a) lattice energies of solids
(b) hydration energies of cations
(c) entropy of solution formation
(d) inter ionic attraction

Key Concepts

Ionic Hydration Energy

This concept describes the energy released when gaseous ions become surrounded by water molecules. In aqueous solutions, higher hydration energy means that ions are more stabilized by solvation. For metal cations, especially those in smaller sizes, a high hydration energy can overcome lattice energy and increase solubility. As the cation size increases down a group, the hydration energy decreases, which can reduce solubility.

Ionic Lattice Energy

Lattice energy is the energy released when oppositely charged ions in the gas phase come together to form a crystalline solid. It is a measure of the strength of the forces holding the ionic lattice together. While high lattice energy favors the stability of the solid, it can make dissolution less favorable because breaking the lattice requires energy. However, in trends like the carbonation of group 2 elements, changes in lattice energy are typically less influential than changes in hydration energy.

Solubility Equilibrium

This refers to the balance between the energy required to break up the ionic lattice and the energy released during solvation of the ions. For an ionic compound, solubility depends on whether the hydration energy can compensate for the lattice energy. A decrease in hydration energy without a corresponding decrease in lattice energy tends to make the dissolution process less favorable, thereby reducing solubility.

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