In each of the following pairs of ionic solids, the ions are arranged into similar lattices. Which one has the largest lattice energy?

(a) CaO or KF

(b) NaF or CsI 

Strategy Questions like this require us to find some basis for comparison. In this particular case, the factors associated with lattice energy have to do with the ions that make up the compound. We have two factors to consider. Smaller ions tend to have stronger coulombic interactions because the distance between the nuclei is smaller, and ions with larger charges have stronger interactions. An examination of these two factors may allow us to predict which substance has the larger lattice energy.