Gold

79

Au

196.966569
  • Name: Gold
  • Symbol: Au
  • Atomic number: 79
  • Atomic weight: 196.966569
  • CAS Registry ID: 7440-57-5
  • Group name: Coinage metal
  • Period number: 6
  • Block: d-block
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Description

Gold is a transition metal that has a bright yellow color in its natural solid state. It is a rare and precious metal, and it is one of the most ductile and malleable of all the metals. Gold has an atomic weight of 196.966569, a melting point of 1947.52 °F, and a boiling point of 5173 °F. Gold is most commonly used for monetary and jewelry purposes. Gold is also used as a solder material, as a component in dentistry fillings and bridges, as a coloring agent in some glass, and in electronics.

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Isolation

Gold is found in its free native state in nature, but it is very rare. More often, gold is obtained by extraction and isolation from ore which contains gold.

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The extraction process of gold is expensive and sometimes causes severe environmental damage; the isolation of gold is hardly ever produced on a small scale laboratory basis due to the expense and chemical steps involved. The beginning the extraction and isolation process of gold begins with mining ore which contains particles of gold. The ore is then subject to a variety of processes depending on what type of ore the gold is found in. Many processes crush the ore to a powder, than dissolve the rock powder in a solution of cyanide that is open to the air. A cyanide gold complex is formed, and addition of zinc powder to the complex causes pure gold to precipitate out of the solution. High purity gold is isolated using such procedures as the Wohlwill process and the Miller process. The Wohlwill process uses an electrochemical process, and the Miller process uses a chemical process to further purify gold.
General
Name Gold
Symbol Au
Number 79
Chemical series transition metals
Group 11
Period 6
Block 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
Atomic properties
Crystal structure cubic face centered
Oxidation states −1, 1, 2, 3, 4, 5 (amphoteric oxide)
Electronegativity 2.54 (scale Pauling)
Ionization energies 1st: 890.1 kJ/mol
(more) 2nd: 1980 kJ/mol
(more)
Atomic radius 135 pm
Atomic radius (calc.) 174 pm
Covalent radius 144 pm
Van der Waals radius 166 pm
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)
Critical point
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
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
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

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