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From Wikipedia, the free encyclopedia
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
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
(amphoteric oxide)
Electronegativity
2.54 (scale Pauling)
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
diamagnetic
Electrical resistivity
(20?°C) 22.14 n?O·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
e
0.227
195Pt
196Au
syn
6.183 d
e
1.506
196Pt
?-
0.686
196Hg
197Au
100%
Au is stable with 118 neutrons
198Au
syn
2.69517 d
?-
1.372
198Hg
199Au
syn
3.169 d
?-
0.453
199Hg
References
Gold (pronounced /'go?ld/) is a chemical element with the symbol Au (from the Latin aurum, meaning shining dawn) 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 jewelry. 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 a bright yellow color traditionally considered attractive.
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.
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