gold

This article is about the metal. For the color, see Gold (color). For other uses, see Gold (disambiguation). 79 platinum ← gold → mercury Ag ↑ Au ↓ Rg Periodic Table - Extended Periodic Table General Name, Symbol, Number gold, Au, 79 Element category 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 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 Crystal structure face centered cubic Oxidation states -1, 1, 2, 3, 4, 5 (amphoteric oxide) Electronegativity 2.54 (Pauling scale) Ionization energies 1st: 890.1 kJ/mol 2nd: 1980 kJ/mol Atomic radius 144  pm Covalent radius 136±6  pm Van der Waals radius 166 pm Miscellaneous Magnetic ordering diamagnetic 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 Tensile strain 0.00157   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 References 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 in jewelry, in sculpture, and for ornamentation 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. At STP 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 1.1 Color of gold 2 Applications 2.1 As the metal 2.1.1 Medium of monetary exchange 2.1.2 Jewelry 2.2 Medicine 2.3 Food and drink 2.4 Industry 2.5 Electronics 2.6 Other 2.7 As gold chemical compounds 3 History 4 Occurrence 5 Isotopes 6 Production 7 Consumption 8 Price 8.1 Price records 8.2 Long term price trends 9 Compounds 9.1 Less common oxidation states: Au(-I), Au(II), and Au(V) 9.2 Mixed valence compounds 10 Symbolism 11 Toxicity 12 See also 13 Footnotes 14 Bibliography 15 External links Characteristics Gold nuggets found in Arizona Gold is the most malleable and ductile of all metals; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold leaf can be beaten thin enough to become translucent. The transmitted light appears greenish blue, because gold strongly reflects yellow and red.[2] Gold readily creates alloys with many other metals. These alloys can be produced to modify the hardness and other metallurgical properties, to control melting point or to create exotic colors (see below). Gold is a good conductor of heat and electricity and reflects infra red radiation strongly. Chemically, it is unaffected by air, moisture and most corrosive reagents, and is therefore well-suited for use in coins and jewelry and as a protective coating on other, more reactive, metals. However, it is not chemically inert. Free halogens will react with gold, and aqua regia dissolves it via formation of chlorine gas which attacks gold to form the chloraurate ion. Gold also dissolves in alkaline solutions of potassium cyanide and in mercury, forming a gold-mercury amalgam. Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate. High quality pure metallic gold is tasteless; in keeping with its resistance to corrosion (it is metal ions which confer taste to metals). In addition, gold is very dense, a cubic meter weighing 19300 kg. By comparison, the density of lead is 11340 kg/m³, and that of the densest element, osmium, is 22610 kg/m³. Color of gold Different colors of Ag-Au-Cu alloys The color of pure gold is metallic yellow. Gold, caesium and copper are the only metallic elements with a natural color other than gray or white. The usual gray color of metals depends on their "electron sea" that is capable of absorbing and re-emitting photons over a wide range of frequencies. Gold reacts differently, depending on subtle relativistic effects that affect the orbitals around gold atoms. [3][4] Common colored gold alloys such as rose gold can be created by the addition of various amounts of copper and silver, as indicated in the diagram below. Alloys containing palladium or nickel are also important in commercial jewelry as these produce white gold alloys. Less commonly, addition of manganese, aluminium, iron, indium and other elements can produce more unusual colors of gold for various applications.[5]