(a) Does the lattice energy of an ionic solid increase or decrease (i) as the charges of the ions increase, (ii) as the sizes of the ions increase?

Key Concepts

Lattice Energy

Lattice energy is the energy released when gaseous ions combine to form an ionic solid. It is a measure of the strength of the forces between the ions in an ionic compound. Higher lattice energy indicates a more stable ionic solid, as it reflects stronger ionic bonds resulting from the electrostatic attraction between oppositely charged ions.

Charge of Ions

The charge of ions significantly affects lattice energy. As the charges of the ions increase, the electrostatic attraction between them becomes stronger, leading to a higher lattice energy. For example, a compound formed from divalent ions (e.g., Mg²⁺ and O²⁻) will have a greater lattice energy than one formed from monovalent ions (e.g., Na⁺ and Cl⁻) due to the increased charge.

Size of Ions

The size of the ions also influences lattice energy. As the size of the ions increases, the distance between the centers of the ions increases, which weakens the electrostatic attraction and results in lower lattice energy. Therefore, larger ions lead to a decrease in lattice energy, as seen when comparing NaCl to KCl, where K⁺ is larger than Na⁺.