Question

Why is the `NaCl` boiling point high?

Answer 1

Because sodium chloride has a non-molecular structure, stabilized by strong electrostatic forces that persist throughout the lattice.

Explanation:

In solid sodium chloride there are no discrete sodium chloride molecules. Each sodium ion is electrostatically bound to EVERY other chloride ion in the lattice. Of course, it is electrostatically repelled by every other sodium ion, but if you sum these interactions up, which can certainly be done, the net electrostatic interaction is attractive.

Given this non-molecular structure we would expect high melting points, and also high boiling points, which are indeed observed.

A related question is `"why does sodium chloride exhibit water solubility?"` Now sodium chloride is soluble to some extent in water, and the water molecules can make ion-dipole bonds with individual sodium and chloride ions. The dissolution is slightly endothermic, meaning that the lattice enthalpy of sodium chloride is almost precisely balanced by the ion-dipole bonds made between the ions and the solvent molecules.