Because the extent of ionic charge is more important than ionic radius in calculating the lattice energy of ionic compounds. Because the ionic charge of the N3-ion is greater than that of the F-ion, the Na3N molecule has a higher lattice energy than the NaF complex.
The lattice energy increases when the ion charge variable is increased. As a result, ions with higher charge values generate ionic compounds with higher lattice energies. As a result, ions with lower charges lower the lattice energies of their compounds.
