1. The problem statement, all variables and given/known data Which one of the following ionic compounds has the largest lattice energy? NaCl CaO Li2O CaCl2 2. Relevant equations Ionic/Atomic size The smaller the ionic size, the larger the lattice energy. Size increases from right to left, increases top to bottom of periodic table 3. The attempt at a solution I've tried to compare the like ionic compounds, such as NaCl with CaCl2 but I can't seem to figure out which is bigger--Na+ or Ca2+ Am I approaching this incorrectly?