Gold is a chemical element with the symbol Au (from the Latin aurum) and atomic number 79. It is a highly sought-after precious metal which, for many centuries, has been used as money, a store of value and in jewelery. The metal occurs as nuggets or grains in rocks, underground "veins" and in alluvial deposits. It is one of the coinage metals. Gold is dense, soft, shiny and the most malleable and ductile of the known metals. Pure gold has an attractive bright yellow colour and is one of only two coloured metal elements, the other being copper. All other metals are silver or grey.

Gold forms the basis for a monetary standard used by the International Monetary Fund (IMF) and the Bank for International Settlements (BIS). The ISO currency code of gold bullion is XAU. Modern industrial uses include dentistry and electronics, where gold has traditionally found use because of its good resistance to oxidative corrosion.

Chemically, gold is a trivalent and univalent transition metal. Gold does not react with most chemicals, but is attacked by chlorine, fluorine, aqua regia and cyanide. Gold dissolves in mercury, forming amalgam alloys, but does not react with it. Gold is insoluble in nitric acid, which will dissolve silver and base metals, and this is 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. interesting

Gold Compounds
The most common gold compounds are auric chloride (AuCl3) and chlorauric acid (HAuCl4). A mixture of one part nitric acid with three of hydrochloric acid is called aqua regia (because it dissolved gold, the King of Metals). It is unaffected by air and most reagents. It is found free in nature and associated with quartz, pyrite and other minerals. Two thirds of the world's supply comes from South Africa, and 2/3 of USA production is from South Dakota and Nevada. Gold is found in sea water, but no effective economic process has been designed (yet) to extract it from this source.

Common reference compound: no defined reference.
Isotope 1       Isotope 2       Isotope 3
Isotope           197Au                       
Natural abundance /%       100                
Spin (I)           3/2                 
Frequency relative to 1H = 100 (MHz)    1.754000                  Receptivity, DC, relative to 13C = 1.00   0.158             
Magnetogyric ratio, γ (107 rad T-1 s-1)   0.473060                  
Magnetic moment, μ (μN) 0.191271                  
Nuclear quadrupole moment, Q (barn)   0.547             
Line width factor, 1056l (m4)         0.29
Common reference compound: no defined reference.      
Isotope 1       Isotope 2       Isotope 3
Isotope           197Au                       
Natural abundance /%       100                
Spin (I)           3/2                 
Frequency relative to 1H = 100 (MHz)    1.754000                  
Receptivity, DP, relative to 1H = 1.00      0.0000277               
Receptivity, DC, relative to 13C = 1.00   0.158             
Magnetogyric ratio, γ (107 rad T-1 s-1)   0.473060                  
Magnetic moment, μ (μN) 0.191271                  
Nuclear quadrupole moment, Q (barn)   0.547             
Line width factor, 1056l (m4)         0.29

Temperatures
            Melting point [/K]: 1337.33 [or 1064.18 °C (1947.52 °F)]
            Boiling point [/K]: 3129 [or 2856 °C (5173 °F)] (liquid range: 1791.67 K)

General
Name, Symbol, Number gold, Au, 79
Chemical series transition metals
Group, Period, Block 11, 6, d
Appearance metallic yellow
Standard atomic weight 196.966569(4)  g·mol−1
Electron configuration [Xe] 4f14 5d10 6s1
Electrons per shell 2, 8, 18, 32, 18, 1

Physical properties
Phase solid
Density (near r.t.) 19.3  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
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
Crystal structure cubic face centered
Oxidation states −1, 1, 2, 3, 4, 5, 6, 7
(amphoteric oxide)
Electronegativity 2.54 (Pauling scale)
Ionization energies 1st: 890.1 kJ/mol
2nd: 1980 kJ/mol
Atomic radius 135  pm
Atomic radius (calc.) 174  pm
Covalent radius 144  pm
Van der Waals radius 166 pm

Miscellaneous
Magnetic ordering no data
Electrical resistivity (20 °C) 22.14 n Ω·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.) (hard-drawn)
2030  m·s−1
Young's modulus 78  GPa
Shear modulus 27  GPa
Bulk modulus 220  GPa
Poisson ratio 0.44
Mohs hardness 2.5
Vickers hardness 216  MPa
Brinell hardness ? 2450  MPa
CAS registry number 7440-57-5

Selected 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% Au is stable with 118 neutrons
198Au syn 2.69517 d β- 1.372 198Hg
199Au syn 3.169 d β- 0.453 199Hg