Gold Element Facts

79 Au 196.9665 Gold General | States | Energies Oxidation & Electrons | Appearance & Characteristics Reactions | Compounds | Radius | Conductivity Abundance & Isotopes Two faces of gold: Nasa message to aliens carried by the Voyager spacecraft and, on the right, a pirate treasure coin.

General:

Name: Gold	Symbol: Au
Type: Transition Metal	Atomic weight: 196.9665
Density @ 293 K: 19.32 g/cm3	Atomic volume: 10.2 cm3/mol
Discovered: Gold has been known and highly valued since ancient times. The chemical symbol Au comes from the Latin word for gold 'aurum', meaning 'shining dawn'.

States

State (s, l, g): solid
Melting point: 1337.33 K   (1064.18 oC)	Boiling point: 3123 K   (2850 oC)

Energies

Specific heat capacity: 0.128 J g-1 K-1	Heat of atomization: 368 kJ mol-1
Heat of fusion: 12.550 kJ mol-1	Heat of vaporization (sublimation): 334.40 kJ mol-1
1st ionization energy: 890.1 kJ mol-1	2nd ionization energy: 1980 kJ mol-1
3rd ionization energy: kJ mol-1	Electron affinity: 222.752 kJ mol-1

Oxidation & Electrons

Shells: 2,8,18,32,18,1	Electron configuration: [Xe] 4f14 5d10 6s1
Minimum oxidation number: -1	Maximum oxidation number: 5
Min. common oxidation no.: 0	Max. common oxidation no.: 3
Electronegativity (Pauling Scale): 2.54	Polarizability volume: 6.1 Å3

Appearance & Characteristics

Structure: fcc: face-centered cubic	Color: golden yellow
Harmful Effects: Gold is considered to be non-toxic.	Hardness: 2.5 mohs
Characteristics: Gold is a soft, yellow, very dense metal with a beautiful lustrous sheen. It is the most malleable and ductile of all elements and a single gram can be beaten into a sheet of one square meter. It is unaffected by air, water, alkalis and all acids except aqua regia (a mixture of hydrochloric acid and nitric acid) which can dissolve gold. Gold does react with halogens. Unusually for a metal, gold can also form compounds (aurides) in which its oxidation number is negative (-1). Gold is a good conductor of heat and electricity.
Uses: Gold is used extensively for jewelry, decoration, dental work, coinage and for plating. The gold content of gold alloys is measured in carats (k), pure gold being designated as 24k. Many satellites carry gold-coated mylar sheets as a solar heat shield because gold is inert and is an excellent reflector of radiation. Similarly astronaut's helmet visors are coated with a thin layer of gold to guard against dangerous effects of solar radiation. Gold is used widely in microelectronic circuits to ensure reliable, corrosion-resistant and static-free performance. The isotope 198Au, with a half-life of 2.7 days, is used for treating cancer. Gold flake is added to some gourmet sweets and drinks. Chloroauric acid (HAuCl4) is used in photography for toning the silver image.

Reactions

Reaction with air: none	Reaction with 6 M HCl: none
Reaction with 3 M HNO3: none	Reaction with 6 M NaOH: none

Compounds

Oxide(s): Au2O3	Chloride(s): AuCl2, [AuCl3]2 (auric chloride)
Hydride(s): none

Radius

Atomic radius: 135 pm	Ionic radius (1+ ion): 151 pm
Ionic radius (2+ ion): pm	Ionic radius (3+ ion): 99 pm
Ionic radius (2- ion): pm	Ionic radius (1- ion): pm

Conductivity

Thermal conductivity: 318 W m-1 K-1

Electrical conductivity: 48.8 x 106 S m-1

Abundance & Isotopes

Abundance earth's crust: 3.1 parts per billion by weight, 0.3 parts per billion by moles

Abundance solar system: 1 part per billion by weight, 10 parts per trillion by moles

Cost, pure: 4400 $/100g

Cost, bulk: 1200 $/100g

Source: Gold is found underground and in rivers. The river deposits arise when gold that was rock-bound is released by erosion of the surrounding rock by running water. Gold is usually found as a metal alloyed to some degree with silver or sometimes with mercury as an amalgam. Gold sizes found on Earth range from sizeable nuggets through tiny grains in alluvial (river) deposits to microscopic pieces in rocks. About two-thirds of the world's gold output comes from mines in South Africa. Commercially, gold is purified by cyaniding, amalgamating, and smelting processes. Further refining, which produces nearly pure gold, is usually by electrolysis.

Isotopes: Gold has 35 isotopes whose half-lives are known, with mass numbers 171 to 205. Of these only one stable, 197Au.