Final answer:
Lattice energy is directly proportional to the product of the ion charges and inversely proportional to the internuclear distance.
Step-by-step explanation:
Lattice energy is directly proportional to the product of the ion charges and inversely proportional to the internuclear distance. In other words, lattice energy increases as the charges of the ions increase and decreases as the distance between the ions increases.
For example, in a series of compounds with the same cation, if the anion becomes larger, the internuclear distance increases, and the lattice energy decreases. Similarly, if the cation becomes larger, the internuclear distance increases, and the lattice energy decreases.