Electrostatic force of attraction between cation and anion is called Lattice energy.
Lattice energy (F)=K
q1q2
r2
q1 and q2 are the charges of cations and anion. So Lattice energy depends on the charges of ions. r= distance between center of ions And, r=r++r−where r+=radius of cation and r−=radius of anion So, more the size of ions less the value of Lattice energy.