Gold Ions

The metal forms univalent and tervalent ions characterized by their low electroaffinity. This property finds expression in the formation of complex derivatives with most anions, in the comparatively low solubility of the halides and oxides, and in the hydrolytic decomposition of its salts.

Aurous Ion

This ion is known almost exclusively in the form of complex anions of the type Au(CN)₂'. Aurous compounds are converted by water into auric compounds, with separation of metallic gold, a reaction facilitated by the presence of halogen ions, complex derivatives of auric ion being formed:

3Au^• ⇔ Au^•••+2Au.

Auric Ion

This ion is characterized by its strong tendency to form complex derivatives, and also by its low electroaffinity. This second property accords with the ease of liberation of the metal by the action of numerous reducers, examples of this phenomenon being cited in the section on the modifications of gold. The reddish-violet stain produced on the skin by gold solutions is due to deposition of the metal. Many reductions are accelerated by the action of light, and many of them take place more rapidly in alkaline solution than in acidic solution.

Although derivatives of bivalent gold are known, there is no certainty as to the existence of an Au^•• ion.