Question

(a) Define the term lattice energy. (b) Which factors govern the magnitude of the lattice energy of an ionic compound?

Short answer

(a) Lattice energy is defined as the energy required to separate one mole of a solid ionic compound into its gaseous constituent ions. (b) Two factors govern the magnitude of lattice energy in an ionic compound: 1. Charge of the ions: Lattice energy increases with higher charges on the ions. 2. Size of the ions: Smaller ions result in higher lattice energy, while larger ions lead to lower lattice energy.

Step-by-step solution

(a) Definition of Lattice Energy

Lattice energy can be defined as the energy required to separate one mole of a solid ionic compound into its gaseous constituent ions. In other words, it is the energy change associated with breaking the ionic bonds in an ionic compound.

(b) Factors Governing the Magnitude of Lattice Energy

There are two main factors that govern the magnitude of lattice energy in an ionic compound: 1. Charge of the ions: The magnitude of lattice energy increases with the increase in the charges of the ions. As the charge increases, the electrostatic attraction between the ions becomes stronger, and more energy is required to separate them. In general, if the charges of the cation and anion are increased, the lattice energy will also increase. 2. Size of the ions: The magnitude of lattice energy also depends on the size of the ions participating in the ionic bond. Smaller ions result in a higher magnitude of lattice energy as they can come closer together, increasing the electrostatic force between them. Larger ions have a lower magnitude of lattice energy as they cannot come as close together due to their size, resulting in weaker ionic attractions. As a summary, the lattice energy of an ionic compound depends on the charges and sizes of the ions involved in the ionic bond. A higher charge and smaller size will both lead to a larger magnitude of lattice energy.