Gold
[Xe] 4f¹⁴ 5d¹⁰ 6s¹ · 2 · 8 · 18 · 32 · 18 · 1
A metal that does not tarnish, does not corrode and reacts with almost nothing. That chemical indifference, plus scarcity, made gold the universal measure of value for five thousand years.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 79
- Atomic mass
- 196.967 а.е.м.
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s¹
- Electrons per shell
- 2 · 8 · 18 · 32 · 18 · 1
- Block
- d-block
- Group
- Copper group
- Period
- 6
- Electronegativity (Pauling)
- 2.54
- Electronegativity (Allen)
- 1.92
- Atomic radius
- 174 pm
- Covalent radius
- 136 pm
- Van der Waals radius
- 166 pm
- Ionisation energy 1
- 890.1 kJ/mol
- Ionisation energy 2
- 1 980 kJ/mol
- Electron affinity
- 222.8 kJ/mol
- Common oxidation states
- +1, +3
- Oxidation states
- -3, -2, -1, +1, +2, +3, +5
Physical properties
- State at 25 °C
- solid
- Density
- 19.3 g/cm³
- Melting point
- 1 337.33 K · 1 064.2 °C
- Boiling point
- 3 243 K · 2 969.9 °C
- Speed of sound
- 2 030 m/s
Thermal properties
- Heat of fusion
- 12.55 kJ/mol
- Heat of vaporisation
- 342 kJ/mol
- Specific heat capacity
- 0.129 J/(g·K)
- Thermal conductivity
- 318 W/(m·K)
Mechanical properties
- Young's modulus
- 78 GPa
- Shear modulus
- 27 GPa
- Bulk modulus
- 180 GPa
- Poisson ratio
- 0.44
- Mohs hardness
- 2.5
- Brinell hardness
- 25 MPa
Electrical and magnetic properties
- Electrical resistivity
- 22.14 nΩ·m
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- face-centred cubic (fcc)
- Lattice constants
- a = 407.82 pm
Abundance
- In the crust
- 0.004 mg/kg
- In the ocean
- 4·10⁻⁶ mg/L
- In the universe
- 0.006 mg/kg
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 197Au | 100 % | stable | — |
Gold-197 is the only stable isotope. Gold-198 was used in brachytherapy.
Discovery
- Year of discovery
- known since antiquity
- Discovered by
- known since antiquity
- Where
- no data
- Origin of the name
- from Latin aurum (shining dawn)
History
Gold has been worked since the sixth millennium BCE — the Varna hoard, 6500 years old, holds the oldest gold artefacts known. Latin aurum means shining dawn.
Where it occurs
0.004 mg/kg of the crust. It occurs almost entirely native. All the gold ever mined would fit in a cube about 22 metres on a side.
How it is produced
By cyanide leaching of crushed ore, then zinc precipitation or carbon adsorption. The largest producers are China, Australia and Russia.
Role in living things
No biological role. Gold compounds were used for rheumatoid arthritis before modern drugs.
Safety
Metallic gold is harmless and permitted as food additive E175. The cyanide extraction process is environmentally dangerous: tailings dam failures have caused major disasters.
Uses
- Investment and central bank reserves — over half of all gold
- Jewellery
- Electronic contacts and connectors: gold does not oxidise, so it does not lose conductivity
- Infrared reflective coatings on spacecraft
- Dentistry and colloidal gold in diagnostic tests
Curiosities
- Gold is the only yellow metal; the cause is relativistic effects that contract the 6s orbital and shift its absorption into the blue.
- One gram of gold can be drawn into a wire about 2.4 kilometres long.
- A gold layer a hundred nanometres thick coats the James Webb telescope's mirrors.
- Earth's gold was probably delivered by asteroid bombardment after the core had already formed.
- Seawater holds some 20 million tonnes of gold, but extracting it costs more than it is worth.