1.2 Charge balance (or electrical stability)

The requirement for charge balance or electrical stabilty in silicate and other ionic compounds means that the sum of positive and negative charges on the ions must balance. This is not achieved by pairing of individual cations and anions; but rather the positive charge on a cation is divided equally by the surrounding anions, the number of which is determined by the relative sizes of the ions (i.e., the coordination number of the cation). This is summarised in one of Pauling's rules " in a stable structure the total strength of valency bonds which reach an anion from all the neibouring cations is equal to the charge on the anion".