electrostatic valence rule Edit
For a given cation, Pauling defined[2] the electrostatic bond strength to each coordinated anion as , where z is the cation charge and ν is the cation coordination number. A stable ionic structure is arranged to preserve local electroneutrality, so that the sum of the strengths of the electrostatic bonds to an anion equals the charge on that anion.
where is the anion charge and the summation is over the adjacent cations. For simple solids, the are equal for all cations coordinated to a given anion, so that the anion coordination number is the anion charge divided by each electrostatic bond strength. Some examples are given in the table.