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    gold (Au)

    gold
    Native gold. Credit: U.S. Geological Survey
    A soft, bright yellow, corrosion-resistant element, one of the family of noble metals, and the most malleable and ductile metal. It occurs in group IB of the periodic table and is a transition element Gold occurs native, typically as small particles in quartz and pyrite but also as deposits after erosion of the quartz and sometimes as nuggets. It also occurs in tellurides in the same minerals. It is recovered by mining, panning, or sluicing, and is extracted with potassium cyanide in the presence of peroxide or air to give the [Au(CN)2]- ion or by forming an amalgam, and is refined with electrolysis.

    Gold is not attacked by oxygen or by single alkalis or acids (except H2SeO4). It dissolves in aqua regia and in cyanide and halogen solutions and is attacked by fluorine. It forms mainly trivalent and monovalent salts. Gold (III) chloride is used as a toner in photography. For more, see "Chemistry of gold" below.

    Gold is a good thermal and electrical conductor, is generally alloyed to increase its strength, and is used as an international monetary standard, in jewelry, for decoration, in dentistry, and as a plated coating on a wide variety of electrical and mechanical components. It is also turned into thin foil, only 0.1μm thick, called gold leaf, by beating it between vellum and animal skins. Gold leaf is used for decorative gilding, lettering on leather-bound books, and for coating artificial satellites, etc., to reflect infrared radiation. Gold can also be welded in a thin layer to another metal (rolled gold). For most uses gold is too soft, and is alloyed with other noble metals, the proportion of gold being measured in carats.


    atomic number 79
    relative atomic mass 196.967
    electron configuration 1s22s22p63s23p64s23d104p65s2
    4d105p66s24f145d9
    metallic radius 144 pm
    oxidation states +5, +3, +2, +1
    relative density 19.32
    melting point 1,063°C (1,945°F)
    boiling point 2,966°C (5,371°F)


    Chemistry of gold

    Gold is an element of the copper group. Of its oxidation states, the +5 state is found only in AuF5, and hexafluoroaurates(V). The common states are +3 (generally square planar) and +1 (generally linear). Both +3 and +1 states form extensive ranges of complexes particularly with soft bases. Organometallic compounds are readily formed. Gold(II) complexes are formed with S-ligands but many compounds which are apparently Au(II) derivatives contain Au(I) and AU(II). Gold forms stable metal-metal bonds with other metals and cluster compounds, e.g. Au11I3L7 or 8 (L = phosphines) are formed on reduction.


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       • INORGANIC CHEMISTRY



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