Gallium
[Ar] 3d¹⁰ 4s² 4p¹ · 2 · 8 · 18 · 3
A metal that melts in your hand: gallium's melting point is 29.8 °C. Mendeleev predicted it as eka-aluminium four years before it was found, and the match of predicted properties settled the case for the periodic law.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 31
- Atomic mass
- 69.723 а.е.м.
- Electron configuration
- [Ar] 3d¹⁰ 4s² 4p¹
- Electrons per shell
- 2 · 8 · 18 · 3
- Block
- p-block
- Group
- Boron group
- Period
- 4
- Electronegativity (Pauling)
- 1.81
- Electronegativity (Allen)
- 1.76
- Atomic radius
- 136 pm
- Covalent radius
- 122 pm
- Van der Waals radius
- 187 pm
- Ionisation energy 1
- 578.8 kJ/mol
- Ionisation energy 2
- 1 979.3 kJ/mol
- Ionisation energy 3
- 2 963 kJ/mol
- Ionisation energy 4
- 6 180 kJ/mol
- Electron affinity
- 28.9 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- -5, -4, -2, -1, +1, +2, +3
Physical properties
- State at 25 °C
- solid
- Density
- 5.91 g/cm³
- Melting point
- 302.91 K · 29.8 °C
- Boiling point
- 2 673 K · 2 399.9 °C
- Speed of sound
- 2 740 m/s
Thermal properties
- Heat of fusion
- 5.59 kJ/mol
- Heat of vaporisation
- 256 kJ/mol
- Specific heat capacity
- 0.371 J/(g·K)
- Thermal conductivity
- 40.6 W/(m·K)
Mechanical properties
- Young's modulus
- 9.8 GPa
- Shear modulus
- 6.7 GPa
- Bulk modulus
- no data
- Poisson ratio
- 0.47
- Mohs hardness
- 1.5
- Brinell hardness
- 60 MPa
Electrical and magnetic properties
- Electrical resistivity
- 270 nΩ·m
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 1.083 K
Crystal structure
- Crystal structure
- orthorhombic
- Lattice constants
- a = 451.97 pm · b = 766.33 pm · c = 452.6 pm
Abundance
- In the crust
- 19 mg/kg
- In the ocean
- 3·10⁻⁵ mg/L
- In the universe
- 0.1 mg/kg
- In the human body
- 0 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 69Ga | 60.108 % | stable | — |
| 71Ga | 39.892 % | stable | — |
Gallium-67 and gallium-68 are both used in nuclear medicine: the first for inflammation scintigraphy, the second in PET tumour imaging.
Discovery
- Year of discovery
- 1875
- Discovered by
- Paul-Émile Lecoq de Boisbaudran
- Where
- France
- Origin of the name
- from Gallia, the Latin name for France
History
Lecoq de Boisbaudran discovered gallium in 1875 from spectral lines in zinc blende. Mendeleev read the paper and wrote to say the density was wrong — and was right: after further purification it matched his prediction.
Where it occurs
19 mg/kg of the crust, with no ore of its own. It is recovered alongside bauxite processing and zinc concentrates.
How it is produced
By electrolysis from the alkaline liquors of the Bayer process. World output is a few hundred tonnes a year.
Role in living things
No biological role. Gallium ions are close in size to iron's, so organisms sometimes mistake one for the other — the basis of experimental antimicrobials.
Safety
Of low toxicity, but gallium metal destroys aluminium: it seeps along grain boundaries and turns a strong alloy into crumbling powder.
Uses
- Gallium nitride for blue and white LEDs and for high-power electronics
- Gallium arsenide in microwave devices, space solar cells and laser diodes
- Low-melting alloys, including non-toxic replacements for mercury
- Liquid-metal heat transfer
Curiosities
- A gallium spoon melts in a cup of hot tea — the classic party trick.
- The match between Mendeleev's eka-aluminium and real gallium is what won the periodic law general acceptance.
- Gallium is restricted on aircraft in some jurisdictions because it attacks aluminium structures.
- Blue LEDs built on gallium nitride won the 2014 Nobel Prize in Physics.