Question #8a58d

Common binary salts such as #M^+X^-# are non-molecular substances, whose particles are held together by strong electrostatic forces. Each metal particle #M^+# in a close-packed binary salt #MX# is electrostatically attracted to 6 negatively charged ions #X^-#, and of course is attracted to every other negatively charged particle in the ionic lattice (of course the electrostatic force of attraction operates on an inverse square law).

While of course there is a electrostatic repulsive force between like charges, if you sum up all the attractive forces and all the negative forces, an overall attractive force results in the ionic lattice of positively and negatively charged ions, and this may be quantitatively assessed by the lattice enthalpy of the ionic solid. Ionic solids tend to have high lattice enthalpies, and hence high temperature is needed to disrupt the lattice, and thus high melting and (very high) boiling points.

To summarize, ionic solids tend to have high melting points, because such solids are non-molecular with very strong forces of attraction between individual particles.