Copper Valency and Ions

Copper is usually considered to exhibit univalency in the cuprous compounds and bivalency in the cupric compounds. Its univalency in the cuprous compounds accords with the position of the metal in the periodic system, and is exemplified by the resemblance of the cuprous halides to the halides of silver and univalent gold, and also by the isomorphism of cuprous sulphide and silver sulphide. The bivalency of the atom in the cupric compounds is in agreement with the properties of many of its derivatives, a typical example being the isomorphism of cupric sulphate with the sulphates of ferrous iron, zinc, magnesium, and manganese.

Besides these two main classes of copper compounds, there appear to be other types of copper derivatives, among them oxides of the formulae Cu₄O, Cu₃O, Cu₂O₃, and CuO₂. The cuprous ion, Cu^•, corresponds with the cuprous compounds, which are colourless in aqueous solution. The cupric ion, Cu^•• corresponds with the cupric compounds, which have a blue, green, violet, yellow, or brown colour in solution.

The cupric ion displays a characteristic power of forming complex derivatives with ammonia and substituted ammonias, an example being the cupric ammonium hydroxides. A great number of other complex derivatives are derived from cuprous or cupric ions. In certain of these compounds both kinds of copper ions are present simultaneously, examples being the complex cupric-cuprous cyanides and sulphites. The cupric ion is characterized by a tendency to form basic salts, a great number having been described.

Both cupric and cuprous salts act as oxidizers, the cupric derivatives being reduced to the cuprous or metallic condition, and the cuprous compounds to metallic copper. Alkaline solutions of cupric salts are employed in oxidation-processes in organic chemistry.