Aluminium
[Ne] 3s² 3p¹ · 2 · 8 · 3
The most abundant metal in the crust, and among the last that humans learned to produce. Until 1886 aluminium cost more than gold; today it is what drinks cans are made of.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 13
- Atomic mass
- 26.982 а.е.м.
- Electron configuration
- [Ne] 3s² 3p¹
- Electrons per shell
- 2 · 8 · 3
- Block
- p-block
- Group
- Boron group
- Period
- 3
- Electronegativity (Pauling)
- 1.61
- Electronegativity (Allen)
- 1.61
- Atomic radius
- 118 pm
- Covalent radius
- 121 pm
- Van der Waals radius
- 184 pm
- Ionisation energy 1
- 577.5 kJ/mol
- Ionisation energy 2
- 1 816.7 kJ/mol
- Ionisation energy 3
- 2 744.8 kJ/mol
- Ionisation energy 4
- 11 577 kJ/mol
- Ionisation energy 5
- 14 842 kJ/mol
- Electron affinity
- 42.5 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- +1, +2, +3
Physical properties
- State at 25 °C
- solid
- Density
- 2.7 g/cm³
- Melting point
- 933.47 K · 660.3 °C
- Boiling point
- 2 743 K · 2 469.9 °C
- Speed of sound
- 5 000 m/s
Thermal properties
- Heat of fusion
- 10.71 kJ/mol
- Heat of vaporisation
- 284 kJ/mol
- Specific heat capacity
- 0.897 J/(g·K)
- Thermal conductivity
- 237 W/(m·K)
Mechanical properties
- Young's modulus
- 70 GPa
- Shear modulus
- 26 GPa
- Bulk modulus
- 76 GPa
- Poisson ratio
- 0.35
- Mohs hardness
- 2.75
- Brinell hardness
- 245 MPa
Electrical and magnetic properties
- Electrical resistivity
- 26.5 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 1.175 K
Crystal structure
- Crystal structure
- face-centred cubic (fcc)
- Lattice constants
- a = 404.95 pm
Abundance
- In the crust
- 82 300 mg/kg
- In the ocean
- 0.002 mg/L
- In the universe
- 50 000 mg/kg
- In the human body
- 0.9 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 26Al | — | 717 116.15 yr | β+ |
| 27Al | 100 % | stable | — |
Aluminium-26, half-life 717 000 years, was a major heat source in the Solar System's first few million years and helped melt the interiors of the earliest asteroids.
Discovery
- Year of discovery
- 1825
- Discovered by
- Hans Christian Ørsted
- Where
- Denmark
- Origin of the name
- from Latin alumen (alum)
History
Ørsted made an impure metal in 1825 and Wöhler improved on it in 1827. The turning point was 1886: Hall and Héroult independently devised electrolysis of alumina in molten cryolite, and the price fell two hundredfold within a decade.
Where it occurs
The third most abundant element in the crust by mass, at 8.2 %. Never free — the Al–O bond is too strong. The industrial ore is bauxite.
How it is produced
The Bayer process turns bauxite into alumina, then the Hall–Héroult process reduces it electrolytically. A tonne of metal takes about 14 MWh, which makes aluminium essentially canned electricity.
Role in living things
No biological role, and plants cannot use it. In acid soils aluminium ions are toxic to roots and limit yields on a third of the world's arable land.
Safety
The metal and its oxide are essentially harmless. Aluminium dust is explosive, and the link to neurodegenerative disease debated in the 1970s has not held up in modern studies.
Uses
- Transport: vehicle bodies, aircraft structures, engine parts
- Packaging: cans, foil, laminates
- Construction: extrusions, roofing, façade panels
- Power transmission lines — per unit mass aluminium beats copper on conductivity
- Thermite mixtures for welding rail
Curiosities
- The Washington Monument was capped with aluminium in 1884 as a display of wealth.
- Aluminium instantly grows an oxide film a few nanometres thick, and that film is what protects it.
- Recycling aluminium takes 5 % of the energy of making it from ore.
- Ruby and sapphire are aluminium oxide with traces of chromium and titanium respectively.