Using the ionic radii given in Table 9.3, estimate the energy to form a mole of Na

Question:

Using the ionic radii given in Table 9.3, estimate the energy to form a mole of Na⁺F^- ion pairs from the corresponding atomic ions.
Table 9.3 lonic Radii (in pm) of Some Main-Group Elements Period 1A 2A ЗА 6A 7A 2 Lit 2+ O?- F- 60 31 140 136 3 Na+ Mg²+ Al3+ S?- Cl- 95 65 50 184 181 4 K+ Са+ Ga3+ Se2- Br- 133 99 62 198 195 Rb+ Sr+ In3+