Au is the chemical symbol for gold, the precious metal with atomic number 79.
The symbol comes from the Latin word aurum, meaning gold. Gold is a chemical element classified as a transition metal, and a neutral gold atom contains 79 protons in its nucleus. Its atomic number is therefore 79, while different isotopes can have different numbers of neutrons.
Gold is valued for its distinctive colour, resistance to corrosion and ability to be shaped. It is highly malleable and ductile: a small quantity can be hammered into extremely thin sheets or drawn into fine wire. Unlike iron or copper, gold does not readily react with oxygen or water, which helps explain why ancient gold objects can survive for thousands of years.
Gold has been used for jewellery, coinage, decoration and religious objects across many civilizations. Modern applications include electronics, dentistry and aerospace components. Pure gold is relatively soft, so jewellery is often alloyed with metals such as silver, copper or palladium. Karat ratings describe the proportion of gold in an alloy, not its mass.