Gold

MELTING POINT: 1,064.18°C

BOILING POINT: 2,808°C

DENSITY: 19.32 g/cm 3

MOST COMMON IONS: Au + , Au 3+ ,

Gold is a soft, malleable yellow metal . If finely divided, it may be black, ruby, or purple. The name of the element is derived from the Anglo-Saxon word geolo, meaning "yellow." The symbol Au is derived from the Latin word aurum, meaning "shining dawn."

Gold is the most malleable and ductile metal known. Approximately 28 grams (1 ounce) of gold can be hammered to form a piece that is 28 square meters (300 square feet). It is a good conductor of heat and electricity, and unreactive in air and most reagents . It forms ionic compounds primarily as a +3 ion; the most common compounds are gold (III) chloride (AuCl 3 ), and chlorauric acid (HAuCl 4 ).

The relative abundance of gold is 0.004 part per million (ppm) in Earth's crust. Deposits of the metal are found in South Africa, Siberia, North America, and South America. Gold has one naturally occurring isotope ( 197 Au) and forty-five synthetic isotopes.

Found in association with quartz or pyrite, gold occurs in veins and is traditionally isolated from rocks by panning or sluicing; these techniques take advantage of gold's high density. A modern method of isolation is the cyanide process, in which gold is leached from crushed rock with an aerated solution of sodium cyanide. The gold then precipitates upon addition of zinc dust and is purified by electrolytic refining.

Gold was used as early as the late Stone Age for ornamental purposes (e.g., jewelry and plating) and more recently as a monetary standard. It is a component of electrical connectors in computer equipment due to its high electrical conductivity. Its unreactivity in air leads to its use for corrosion-free contacts in electrical connections. As an excellent conductor of heat, it is used in the main engine nozzle of the space shuttle. Since gold is the most reflective of all metals, it is used as a coating for space satellites, face shields for astronauts, and windows. Chlorauric acid is used in photography; disodium aurothiomalate is given as a treatment for arthritis.