Gold is a chemical element with the symbol Au (Aurum in Latin) and atomic number 79. It is a dense, soft, malleable and ductile metal with a bright yellow color and luster. Gold is sometimes used as an under-layer in reed switch contacts, but can cause some sticking. Reed Switch leads are plated with Gold to increase the shelf life.
|Standard atomic weight Ar, std(Au)||196.966570(4)|
|Gold in the periodic table|
|Atomic number (Z)||79|
|Electron configuration||[Xe] 4f14 5d10 6s1|
|Electrons per shell||2, 8, 18, 32, 18, 1|
|Phase at STP||solid|
|Melting point||1337.33 K (1064.18 °C, 1947.52 °F)|
|Boiling point||3243 K (2970 °C, 5378 °F)|
|Density (near r.t.)||19.30 g/cm3|
|when liquid (at m.p.)||17.31 g/cm3|
|Heat of fusion||12.55 kJ/mol|
|Heat of vaporization||342 kJ/mol|
|Molar heat capacity||25.418 J/(mol·K)|
|Oxidation states||−3, −2, −1, 0, +1, +2, +3, +5 (an amphoteric oxide)|
|Electronegativity||Pauling scale: 2.54|
|Atomic radius||empirical: 144 pm|
|Covalent radius||136±6 pm|
|Van der Waals radius||166 pm|
|Spectral lines of gold|
|Crystal structure||face-centered cubic (fcc)|
|Speed of sound thin rod||2030 m/s (at r.t.)|
|Thermal expansion||14.2 µm/(m⋅K) (at 25 °C)|
|Thermal conductivity||318 W/(m⋅K)|
|Electrical resistivity||22.14 nΩ⋅m (at 20 °C)|
|Molar magnetic susceptibility||−28.0×10−6 cm3/mol (at 296 K)|
|Tensile strength||120 MPa|
|Young's modulus||79 GPa|
|Shear modulus||27 GPa|
|Bulk modulus||180 GPa|
|Vickers hardness||188–216 MPa|
|Brinell hardness||188–245 MPa|
|Naming||from Latin aurum, meaning gold|
|Discovery||In the Middle East (before 6000 BCE)|
|Main isotopes of gold|
Gold is a chemical element with the symbol Au (from Latin: aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In a pure form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum), naturally alloyed with other metals like copper and palladium and also as mineral inclusions such as within pyrite. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).
Gold is resistant to most acids, though it does dissolve in aqua regia (a mixture of nitric acid and hydrochloric acid), which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic substances, giving rise to the term acid test. Gold also dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, and as the gold acts simply as a solute this is not a chemical reaction.
A relatively rare element, gold is a precious metal that has been used for coinage, jewelry, and other arts throughout recorded history. In the past, a gold standard was often implemented as a monetary policy, but gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was abandoned for a fiat currency system after 1971.
A total of 197,576 tonnes of gold exists above ground, as of 2019[update]. This is equal to a cube with each side measuring roughly 21.7 meters (71 ft). The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry. Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity have led to its continued use in corrosion resistant electrical connectors in all types of computerized devices (its chief industrial use). Gold is also used in infrared shielding, colored-glass production, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine. As of 2017[update], the world's largest gold producer by far was China with 440 tonnes per year.