23.1.5—Explain, in qualitative terms, the effect

Lattice energy reflects electrostatic attraction between oppositely charged ions. Greater ionic charge strengthens attraction, while a smaller internuclear distance also increases the magnitude.

Compare like structures and state what is held constant. Charge effects are often larger than radius effects, but both act through Coulombic attraction and lattice packing.

MgO has a more negative lattice-formation enthalpy than NaCl because Mg²⁺/O²⁻ charges are larger, despite the ions not being identical in size.

Do not claim that radius alone determines lattice energy or compare compounds with different structures without qualification.