الثلاثاء، 22 نوفمبر 2011

gold

Gold

From Wikipedia, the free encyclopedia
platinum ← gold → mercury
Ag

Au

Rg
Appearance
metallic yellow
General properties
Name, symbol,numbergold, Au, 79
Pronunciation/ˈɡld/
Element categorytransition metal
Groupperiod,block116d
Standard atomic weight196.966569(4)
Electron configuration[Xe] 4f14 5d10 6s1
Electrons per shell2, 8, 18, 32, 18, 1 (Image)
Physical properties
Phasesolid
Density (near r.t.)19.30 g·cm−3
Liquid density atm.p.17.31 g·cm−3
Melting point1337.33 K, 1064.18 °C, 1947.52 °F
Boiling point3129 K, 2856 °C, 5173 °F
Heat of fusion12.55 kJ·mol−1
Heat of vaporization324 kJ·mol−1
Molar heat capacity25.418 J·mol−1·K−1
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)164618142021228126203078
Atomic properties
Oxidation states-1, 1, 2, 3, 4, 5
(amphoteric oxide)
Electronegativity2.54 (Pauling scale)
Ionization energies1st: 890.1 kJ·mol−1
2nd: 1980 kJ·mol−1
Atomic radius144 pm
Covalent radius136±6 pm
Van der Waals radius166 pm
Miscellanea
Crystal structureLattice face centered cubic
Magnetic orderingdiamagnetic
Electrical resistivity(20 °C) 22.14 nΩ·m
Thermal conductivity318 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 strength120 MPa
Young's modulus79 GPa
Shear modulus27 GPa
Bulk modulus180 GPa
Poisson ratio0.44
Mohs hardness2.5
Vickers hardness216 MPa
Brinell hardness25 HB MPa
CAS registry number7440-57-5
Most stable isotopes
Main article: Isotopes of gold
isoNAhalf-lifeDMDE (MeV)DP
195Ausyn186.10 dε0.227195Pt
196Ausyn6.183 dε1.506196Pt
β0.686196Hg
197Au100%197Au is stable with 118 neutrons
198Ausyn2.69517 dβ1.372198Hg
199Ausyn3.169 dβ0.453199Hg
v · d · e · r
Gold (play /ˈɡld/) is a chemical element with the symbol Au (from Latinaurum "gold") and anatomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive solid chemical elements. The metal therefore occurs often in free elemental (native) form, as nuggets or grains in rocks, in veins and in alluvial deposits. Less commonly, it occurs in minerals as gold compounds, usually with tellurium.
Gold resists attacks by individual acids, but it can be dissolved by the aqua regia (nitro-hydrochloric acid), so named because it dissolves gold. Gold also dissolves in alkaline solutions of cyanide, which have been used in mining. Gold dissolves in mercury, formingamalgam alloys. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to confirm the presence of gold in items, giving rise to the term the acid test.
Gold has been a valuable and highly sought-after precious metal for coinage, jewelry, and other arts since long before the beginning of recorded historyGold standards have been the most common basis for monetary policies throughout human history, being widely supplanted by fiat currency only in the late 20th century. Gold has also been frequently linked to a wide variety of symbolisms and ideologies. A total of 165,000 tonnes of gold have been mined in human history, as of 2009.[1] This is roughly equivalent to 5.3 billion troy ounces or, in terms of volume, about 8500 m3, or a cube 20.4 m on a side. The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.[2]
Besides its widespread monetary and symbolic functions, gold has many practical uses indentistryelectronics, and other fields. Its high malleabilityductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity led to many uses of gold, including electric wiring, colored-glass production and even gold leaf eating.

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