How do molecules differ from ionic compounds?
Well, molecules are molecular....
...and thus molecules consist of discrete formula units whose interaction is NOT as strong as the forces of the interaction that binds the molecule together, i.e. covalent bonds. Of course, there are some ATOMIC molecules, and what elements are these? And typically molecules have low to middling melting and boiling points, which reflects the relative weakness of intermolecular force.
On the other hand, ionic compounds are NON-MOLECULAR to a first approximation. They consist of DISCRETE anions or cations that are electrostatically bound to EVERY counterion in the complex.
Of course, each individual ion is REPELLED by every other ion of common charge in the structure, but if you go thru the sum of attractive and repulsive interactions, which may certainly be done quantitatively, attractive forces wins, and these are quantified in the lattice enthalpy of a given ionic solid.
The end result is that ionic substances are non-molecular substances, that tend to have some solubility of polar solvents, are non-conductive in the solid state, and have high melting and boiling points, the which attests to the strength of the ionic interaction.