gold

Heavy, precious, yellow, metallic element, atomic number 79, relative atomic mass 197.0. Its symbol comes from the Latin aurum meaning ‘gold’. It occurs in nature frequently as a free metal (see native metal) and is highly resistant to acids, tarnishing, and corrosion. Pure gold is the most malleable of all metals and is used as gold leaf or powder, where small amounts cover vast surfaces, such as gilded domes and statues.

The elemental form is so soft that it is alloyed for strength with a number of other metals, such as silver, copper, and platinum. Its purity is then measured in carats on a scale of 24 (24 carats is pure gold). It is used mainly for decorative purposes (jewellery, gilding) but also for coinage, dentistry, and conductivity in electronic devices.

Gold has been known and worked from ancient times, and currency systems were based on it in Western civilization, where mining it became an economic and imperialistic goal. In 1990 the three leading gold-producing countries were South Africa, 605.4 tonnes; USA, 295 tonnes; and Russia, 260 tonnes. In 1989 gold deposits were found in Greenland with an estimated yield of 12 tonnes per year.

Although gold is ‘noble’ in that it shows very little chemical reactivity, it can be dissolved in aqua regia (a mixture of nitric and hydrochloric acid). From such solutions, certain gold compounds, such as the chloride AuCl₃, can be prepared.

A Japanese company produced a malleable form of gold in 1995, made of fine gold powder mixed with water and a secret binder. Designers can work with the putty in the same way as clay, but once the putty is fired (at 1,000°C), the water and binder evaporate, leaving the fused gold particles.

The name ‘gold’ is very old and derives from the Germanic form of Indo-European ghel, ‘to shine’ or ‘to gleam’.