Stability Of Metal Ions In Molten Glass: The Definition Of Reduction And Oxidation

The positive charge borne by a metal ion, M2+, under normal chemical conditions such as when dissolved in a glass melt, is always significantly less than the oxidation number, +z. This effect arises through chemical bonding and results in the metal ion receiving (negative) electronic charge from surrounding atoms or ions. However, the acceptance of electric charge by the metal ion does not necessarily mean that it has been reduced. Indeed, it is argued that as the metal ion accepts more electronic charge its tendency for undergoing oxidation increases. In the light of this argument it is essential to consider carefully what is meant by the terms "reduction" and "oxidation" as used in glass chemistry.