Facts, information and data about gold.
Gold is a metallic element, with the following properties:-
- Chemical Symbol: Au
- Atomic Number: 79
- Atomic Weight: 196.96655
- CAS Registry ID (Chemical Abstracts Service registry number): 7440-57-5
- Group number: 11
- Group name: Coinage metal
- Period number: 6
- Block: d-block
- Standard state: solid at 298 K
- Colour: gold, although when finely powdered may appear black, red, or purple.
- Classification: Metallic
- Melting point: 1337.33 °K [or 1064.18 °C = 1947.52 °F
- Boiling point: 3129 °K = 2856 °C = 5173 °F
- Liquid range: 1791.67 °K
- Thermal conductivity [/W m-1 K-1]: 320
- Coefficient of linear thermal expansion [/K-1 multiplied by 106]: 14.2
- Enthalpy of fusion [/kJ mol-1]: 12.5
- Enthalpy of vaporization [/kJ mol-1]: 330
- Enthalpy of atomization [/kJ mol-1]: 368
- Young's modulus [/GPa]: 78
- Rigidity modulus [/GPa]: 27
- Bulk modulus [/GPa]: 220
- Poisson's ratio [no units]: 0.44
- Mineral hardness (Moe's Scale) [no units]: 2.5
- Brinell hardness [/MN m-2]: 2450
- Vickers hardness [/MN m-2]: 216
- Electrical resistivity [/10-8 W m; or mW cm]: 2.2
- Reflectivity [/%]: 95
- Refractive index [no units]: no data
- Density of solid [/kg m-3]: 19300
- Molar volume [/cm3]: 10.21
- Velocity of sound [/m s-1]: 1740
- NMR data
- Isotope 1
- Isotope 197Au
- Natural abundance /% 100
- Spin (I) 3/2
- Frequency relative to 1H = 100 (MHz) 1.754000
- Receptivity, DP, relative to 1H = 1.00 0.0000277
- Receptivity, DC, relative to 13C = 1.00 0.158
- Magnetogyric ratio, g (107 rad T-1 s-1) 0.473060
- Magnetic moment, m (mN) 0.191271
- Nuclear quadrupole moment, Q (barn) 0.547
- Line width factor, 1056l (m4) 0.29
- Electronic Configuration
- The following represents the electronic configuration and its associated term symbol for the ground state neutral gaseous atom. The configuration associated with gold in its compounds is not necessarily the same.
- Ground state electron configuration: [Xe].4f14.5d10.6s1
- Shell structure: 220.127.116.11.18.1
- Term symbol: 2S1/2
Other Information about Gold
Gold is available in many form, including wire, sheet, and foil. It is also used as an investment and store of value in the form of gold bars and gold coins.
Carat Gold ( Karat Gold)
For jewellery use, gold is usually alloyed to improve its working qualities because pure gold is a soft metal. The term carat describes the proportion of gold present in the alloy (24 carats is pure gold).
Gold has long been used in foodstuffs for centuries, usually as extremely thin flakes or leaf. Indian kulfi is one example. It was also used by mediaeval European monarchs and nobility. It is still used in some modern Gourmet foods.
Its e-number is E175.
There are a number of liqueurs containing gold flakes, Well-known examples include Danziger Goldwasser, originally from Gdansk, Poland, which has been produced since at least 1598. Others include Goldstrike from Amsterdam, and Goldschläger.
It has been estimated that all the gold in the world, so far mined and refined, would occupy a single cube of 20 metres per side. It is metallic, with a yellow colour when in a mass, but when finely divided it may be black, ruby, or purple.
Gold is the most malleable and ductile metal; 1 ounce of gold can be beaten out to 300 square feet.
Gold is a good conductor of heat and electricity
Gold is unaffected by air and most reagents.
Although gold is a noble metal, being unaffected by air and most reagents, it will form compounds.
The most common gold compounds being auric chloride (AuCl3) and chlorauric acid (HAuCl4).
A mixture of one part nitric acid with three of hydrochloric acid is called aqua regia, because it dissolves gold, the King of Metals.
Gold is found free in nature and associated with quartz, pyrite and other minerals.
Gold constitutes about 3 parts per billion by weight of the earth's crust.
Two thirds of the world's supply of gold comes from South Africa. US sources include South Dakota and Nevada.
Gold is found in sea water, about 5 grams per million tonnes, although no effective economic process has yet been designed to extract it. You may prefer to think about this figure as about 20.5 kilogrammes per cubic mile, with a value of about US$230,000.
Extraction and Isolation of Gold
It would not normally be necessary to make gold in the laboratory as it is readily available commercially.
Gold can be sourced by panning it from streams.
Panning relies upon the density of gold (which is very high) being much greater than that of the sand and other particulates. It therefore settles to the bottom of the pan. This method is mainly used by small scale producers, mainly individual hobbyists.
Today most gold is extracted from ores. These ores often contain relatively little gold. Some of these processes cause environmental concern. The ore is crushed to a powder so as to expose the small gold particles. These are dissolved by treatment of the rock with cyanide solution in air. The result of this is a gold cyanide complex. Addition of zinc powder to the resulting solution precipitates out the gold.
Reactions - Formulae
4Au + 8NaCN + O2 + 2H2O 4Na[Au(CN)2] + 4NaOH
2Na[Au(CN)2] + Zn 2NaCN + Zn(CN)2 + Au (s)
Of all metals, the only two which are not grey in colour are gold and copper.
There may be more, but our favourite two are:-
In Gold We Trust
Ingot We Trust
A common typographical error for the word gold is GLOD.
Much of the technical data above is taken from the excellent WebElements www.webelements.com website run by Sheffield University.
Nuclear magnetic resonance (NMR) data above is copyright 1996 IUPAC
Index of live spot gold price information on this website.