Gold Au

Discovery

Gold occurs in nature as pure nuggets and flakes, so it was one of the first metals people used. Gold ornaments from the Varna necropolis in Bulgaria date to around 4500 BCE, and ancient Egypt associated gold with the gods and with the eternal life of the pharaohs.

Medieval and early modern alchemists tried to make gold from other metals. They never succeeded, but their experiments developed techniques such as distillation and the preparation of strong acids that later underpinned chemistry. In Korea, the gold crowns of the Silla kingdom are celebrated masterpieces of ancient metalwork. The nineteenth century brought a series of gold rushes in California, Australia and South Africa that redrew population maps.

Origin of the name

The symbol Au comes from aurum, the Latin word for gold. The English word gold is thought to share a Germanic root with words for "yellow".

Main uses

• Jewellery and investment: jewellery is the largest source of demand, followed by bars, coins and central-bank reserves.
• Electronics: gold does not corrode and conducts well, so it plates connectors and forms the fine bonding wires that link chips to their packages.
• Medicine and diagnostics: gold nanoparticles create the red line in many pregnancy and rapid antigen tests. Gold compounds were once used to treat rheumatoid arthritis, and gold alloys are used in dentistry.
• Space and optics: gold reflects infrared light extremely well and coats astronaut visors and the mirrors of the James Webb Space Telescope.

Isotopes

Natural gold consists of a single stable isotope, gold-197. Radioactive gold-198, with a half-life of about 2.7 days, was once used in radiotherapy and imaging. In 2017 gravitational-wave and telescope observations of a neutron-star merger provided strong evidence that such collisions forge heavy elements through rapid neutron capture, changing our understanding of where cosmic gold comes from.

In everyday life

A single gram of gold can be hammered into a leaf covering close to a square metre. Its yellow colour is explained by relativistic effects: inner electrons in heavy atoms move at a significant fraction of the speed of light, shifting how gold absorbs blue light. The freezing point of gold, 1,337.33 K, is one of the defining fixed points of the international temperature scale. All the gold ever mined is estimated at a little over 200,000 tonnes. Metallic gold is essentially non-toxic and is even eaten as decorative leaf, although some people develop allergic reactions to gold.