Gold

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This article is about the metal. For the color, see Gold (color). For other uses, see Gold (disambiguation).

platinum ← gold → mercury Ag ↑ Au ↓ Rg 79Au Periodic table
Appearance
metallic yellow
General properties
Name, symbol, number	gold, Au, 79
Element category	transition metal
Group, period, block	11, 6, d
Standard atomic weight	196.966569(4) g·mol−1
Electron configuration	[Xe] 4f14 5d10 6s1
Electrons per shell	2, 8, 18, 32, 18, 1 (Image)
Physical properties
Phase	solid
Density (near r.t.)	19.30 g·cm−3
Liquid density at m.p.	17.31 g·cm−3
Melting point	1337.33 K, 1064.18 °C, 1947.52 °F
Boiling point	3129 K, 2856 °C, 5173 °F
Heat of fusion	12.55 kJ·mol−1
Heat of vaporization	324 kJ·mol−1
Specific heat capacity	(25 °C) 25.418 J·mol−1·K−1
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	-1, 1, 2, 3, 4, 5 (amphoteric oxide)
Electronegativity	2.54 (Pauling scale)
Ionization energies	1st: 890.1 kJ·mol−1
	2nd: 1980 kJ·mol−1
Atomic radius	144 pm
Covalent radius	136±6 pm
Van der Waals radius	166 pm
Miscellanea
Crystal structure	Lattice face centered cubic
Magnetic ordering	diamagnetic
Electrical resistivity	(20 °C) 22.14 nΩ·m
Thermal conductivity	(300 K) 318 W·m−1·K−1
Thermal expansion	(25 °C) 14.2 µm·m−1·K−1
Speed of sound (thin rod)	(r.t.) 2030 m·s−1
Tensile strength	120 MPa
Shear modulus	27 GPa
Bulk modulus	180 GPa
Poisson ratio	0.44
Mohs hardness	2.5
Vickers hardness	216 MPa
Brinell hardness	? 2450 MPa
CAS registry number	7440-57-5
Most stable isotopes
Main article: Isotopes of gold
iso NA half-life DM DE (MeV) DP 195Au syn 186.10 d ε 0.227 195Pt 196Au syn 6.183 d ε 1.506 196Pt β− 0.686 196Hg 197Au 100% 197Au is stable with 118 neutrons 198Au syn 2.69517 d β− 1.372 198Hg 199Au syn 3.169 d β− 0.453 199Hg
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Gold (pronounced /ˈɡoʊld/) is a chemical element with the symbol Au (Latin: aurum) and an atomic number of 79. It has been a highly sought-after precious metal for coinage, jewelry, and other arts since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is dense, soft, shiny and the most malleable and ductile pure metal known. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. It is one of the coinage metals and formed the basis for the gold standard used before the collapse of the Bretton Woods system in 1971.

At the end of 2006, it was estimated that all the gold ever mined totaled 158,000 tonnes.^[1] This can be represented by a cube with an edge length of just 20.2 meters. Modern industrial uses include dentistry and electronics, where gold has traditionally found use because of its good resistance to oxidative corrosion and excellent quality as a conductor of electricity.

Chemically, gold is a transition metal and can form trivalent and univalent cations upon solvation. Compared with other metals, pure gold is more chemically unreactive, but it is attacked by aqua regia (a mixture of acids), forming chloroauric acid, and by alkaline solutions of cyanide but not by single acids such as hydrochloric, nitric or sulfuric acids. Gold dissolves in mercury, forming amalgam alloys, but does not react with it. Since gold is insoluble in nitric acid which will dissolve silver and base metals, this is exploited as the basis of the gold refining technique known as "inquartation and parting". Nitric acid has long been used to confirm the presence of gold in items, and this is the origin of the colloquial term "acid test", referring to a gold standard test for genuine value.

Contents

[hide]

• 1 Characteristics
• 2 Isotopes
  • 2.1 Color of gold
• 3 Applications
  • 3.1 As the metal
    • 3.1.1 Medium of monetary exchange
    • 3.1.2 Jewelry
  • 3.2 Medicine
  • 3.3 Food and drink
  • 3.4 Industry
  • 3.5 Electronics
  • 3.6 As gold chemical compounds
• 4 History
• 5 Occurrence
• 6 Production
• 7 Consumption
• 8 Price
  • 8.1 Price records
  • 8.2 Long term price trends
• 9 Compounds
  • 9.1 Less common oxidation states
  • 9.2 Mixed valence compounds
• 10 Symbolism
• 11 Toxicity
• 12 State Emblem
• 13 See also
• 14 Footnotes
• 15 Bibliography
• 16 External links

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