Ionic solids consist of cations (+ positive charge) and anions (-negative charge). Discrete ionic molecules do not exist. Instead, a repeating array of molecules are held together by strong Coulombic forces (ionic bonds) between oppositely charged ions adjacent to one another.

The following properties are due to this arrangement:

1. Ionic solids are nonvolatile and have high melting points–ionic bonds must be broken to melt the solid, which separates oppositely charged particles. This requires very high temperature to give the particles enough kinetic energy.

2. Ionic solids do not conduct electricity–the charged ions are fixed in place. When melted or dissolved in solution, the ions become free to move about, enabling electrical conduction.

3. Many ionic compounds are soluble in polar solvents like water and insoluble in non-polar solvents like benzene.

Relative strength of different ionic bonds can be estimated from Coulomb’s Law. Coulomb’s law states that the force is proportional to each of the charges and inversely proportional to the distance squared. Therefore, calcium oxide (CaO, +2 and-2) has a much stronger bond that sodium chloride, NaCl. This manifests in the melting points of each compound (2927C for CaO versus 801C for NaCl). Similar reasoning can be used to compare ionic compounds with varying internuclear distances. Because chloride is smaller than bromide, sodium chloride, NaCl, has a higher melting point (801C) than sodium bromide, NaBr (747C).