Final answer:
MgO has more coulombic energy than NaF due to the higher product of ionic charges in MgO, resulting in a significantly greater lattice energy of 3795 kJ/mol for MgO compared to 910 kJ/mol for NaF.
Step-by-step explanation:
In comparing the coulombic energy of NaF and MgO, we find that MgO has a higher lattice energy. The lattice energy, which is a measure of the strength of bonds in ionic compounds, significantly influences physical properties like melting points, hardness, and solubility. According to data from the CRC Handbook of Chemistry and Physics, the lattice energy of NaF is 910 kJ/mol while that of MgO is substantially higher at 3795 kJ/mol.
This notable difference is primarily because MgO consists of Mg2+ and O2- ions which have a product of charges that is four times greater than that of the Na+ and F- ions in NaF. The high lattice energy of MgO reflects stronger ionic bonds resulting in a compound with higher melting points and lower solubility in water, as compared to NaF. Considering that lattice energy increases with the charge of the ions and is inversely related to the ion size, these findings are consistent with Coulomb's Law, which outlines the force between charged particles.