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Gold

Chemical element, symbol Au and atomic number 79 / From Wikipedia, the free encyclopedia

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Gold is a chemical element; it has symbol Au (from Latin aurum 'gold') and atomic number 79. In pure form, it is a bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal, a group 11 element, and one of the noble metals. It is one of the least reactive chemical elements being second lowest in the Reactivity series. It is a solid under standard conditions.

Quick facts: Gold, Appearance, Standard atomic weight .mw-...
Gold, 79Au
Gold_nugget_%28Australia%29_4_%2816848647509%29.jpg
Gold
AppearanceMetallic yellow
Standard atomic weight Ar°(Au)
Gold in the periodic table
Ag

Au

Rg
platinumgoldmercury
Atomic number (Z)79
Groupgroup 11
Periodperiod 6
Block  d-block
Electron configuration[Xe] 4f14 5d10 6s1
Electrons per shell2, 8, 18, 32, 18, 1
Physical properties
Phase at STPsolid
Melting point1337.33 K (1064.18 °C, 1947.52 °F)
Boiling point3243 K (2970 °C, 5378 °F)
Density (near r.t.)19.3 g/cm3
when liquid (at m.p.)17.31 g/cm3
Heat of fusion12.55 kJ/mol
Heat of vaporization342 kJ/mol
Molar heat capacity25.418 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1646 1814 2021 2281 2620 3078
Atomic properties
Oxidation states−3, −2, −1, 0,[3] +1, +2, +3, +5 (an amphoteric oxide)
ElectronegativityPauling scale: 2.54
Ionization energies
  • 1st: 890.1 kJ/mol
  • 2nd: 1980 kJ/mol
Atomic radiusempirical: 144 pm
Covalent radius136±6 pm
Van der Waals radius166 pm
Color lines in a spectral range
Spectral lines of gold
Other properties
Natural occurrenceprimordial
Crystal structure face-centered cubic (fcc)
Face centered cubic crystal structure for gold

Lattice constant: a = 407.84 pm (at 25 °C)[4]
Speed of sound thin rod2030 m/s (at r.t.)
Thermal expansion14.2 µm/(m⋅K) (at 25 °C)
Thermal conductivity318 W/(m⋅K)
Electrical resistivity22.14 nΩ⋅m (at 20 °C)
Magnetic orderingdiamagnetic[5]
Molar magnetic susceptibility−28.0×10−6 cm3/mol (at 296 K)[6]
Tensile strength120 MPa
Young's modulus79 GPa
Shear modulus27 GPa
Bulk modulus180 GPa[7]
Poisson ratio0.4
Mohs hardness2.5
Vickers hardness188–216 MPa
Brinell hardness188–245 MPa
CAS Number7440-57-5
History
Namingfrom Latin aurum 'gold'
DiscoveryIn the Middle East (before 6000 BCE)
Symbol"Au": from Latin aurum
Isotopes of gold
Main isotopes[8] Decay
abun­dance half-life (t1/2) mode pro­duct
195Au synth 186.01 d ε 195Pt
196Au synth 6.165 d β+ 196Pt
β 196Hg
197Au 100% stable
198Au synth 2.69464 d β 198Hg
199Au synth 3.139 d β 199Hg
Symbol_category_class.svg Category: Gold
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Gold often occurs in free elemental (native state), as nuggets or grains, in rocks, veins, and alluvial deposits. It occurs in a solid solution series with the native element silver (as in electrum), naturally alloyed with other metals like copper and palladium, and 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), forming a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid alone, which dissolves silver and base metals, a property long used to refine gold and confirm the presence of gold in metallic substances, giving rise to the term 'acid test'. Gold dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. Gold also 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,[9][10] gold is a precious metal that has been used for coinage, jewelry, and other work of art throughout recorded history. In the past, a gold standard was often implemented as a monetary policy. 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 the Nixon shock measures of 1971.

In 2020, the world's largest gold producer was China, followed by Russia and Australia.[11] A total of around 201,296 tonnes of gold exists above ground, as of 2020.[12] This is equal to a cube with each side measuring roughly 21.7 meters (71 ft). The world's consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.[13] 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, the production of colored glass, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine.

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