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Aluminium (Al)

Aluminium (symbol Al) is the chemical element with atomic number 13: a post-transition metal, solid at 0 °C, with an atomic mass of 26.982 u. Discovered in 1825 (Hans Christian Ørsted).

Aluminium is the most abundant metal in Earth's crust, but it is bound so tightly to oxygen that we only learned to extract it in the 19th century. Light, rustproof thanks to a thin oxide film, and a good conductor, it has taken over transportation, packaging and construction. Producing it devours electricity, but recycling it takes only about 5% as much.

Key facts

Atomic number

13

Symbol

Al

French name

Aluminium

Atomic mass

26.982 u

Molar mass

26.982 g/mol

Family

Post-transition metals

Position

period 3, group 13, p-block

State at 0 °C

Solid

Melting point

660.3 °C

Boiling point

2,469.9 °C

Density

2.7 g/cm³

Electronegativity (Pauling)

1.61

First ionization energy

578 kJ/mol

Atomic radius

125 pm

Electron configuration

[Ne] 3s² 3p¹

Abundance in Earth's crust

82,300 ppm (3rd most abundant element)

Indicative price

2 $/kg (order of magnitude)

Radioactive

no

Discovery

1825, Hans Christian Ørsted

Origin of the name

From the Latin alumen, alum.

What does aluminium look like?

A light, silvery-white metal (density 2.7, a third that of steel), matte or shiny depending on the finish.

Where is aluminium found?

About 8% of Earth's crust, the third most abundant element after oxygen and silicon. It is found in feldspars, clays and above all bauxite, a rock formed by the weathering of soils in tropical climates.

Natural sources

• Bauxite (gibbsite, boehmite)
• Corundum (ruby, sapphire)
• Cryolite
• Feldspars
• Kaolinite

How is aluminium produced?

Bauxite is refined into alumina (Bayer process), which is then dissolved in molten cryolite and electrolyzed at around 960 °C (Hall-Héroult process). Each tonne takes about 14,000 kWh of electricity. The world produces about 70 million tonnes of primary aluminium a year, nearly 60% of it in China.

Top producers

• China
• India
• Russia
• Canada

What is aluminium used for?

• Transportation: aircraft, cars, trains, bikes.
• Packaging: cans, foil, lids.
• Construction: windows, facades, roofing.
• High-voltage power lines.
• Cookware.

In everyday life

• A drink can
• Aluminium foil
• Window frames
• The casing of some smartphones and laptops
• Coffee capsules

Role in living things

No known biological role despite its abundance. In acidic soils it becomes soluble and toxic to plants. A link with Alzheimer's disease has been suggested but never demonstrated.

Hazards of aluminium

The metal is of low toxicity for healthy people. Fine powders can ignite or explode. Patients on kidney dialysis must avoid excessive intake, because their kidneys cannot clear it. Production generates alkaline “red mud” that is hard to store.

Cosmic origin

• Supernovae: Forged in the cores of massive stars, then scattered when they explode.

History of aluminium

The Dane Hans Christian Ørsted obtained impure aluminium in 1825, and the German Friedrich Wöhler isolated it more successfully in 1827. In 1854, Frenchman Henri Sainte-Claire Deville developed a chemical production method, backed by Napoleon III. In 1886, Paul Héroult in France and Charles Martin Hall in the United States, aged 23 and 22, independently invented the electrolysis process that made it cheap.

Did you know?

• Bauxite takes its name from Les Baux-de-Provence in southern France, where it was identified in 1821.
• The Washington Monument is capped with an aluminium pyramid installed in 1884, when it was still a prestige metal.
• Héroult and Hall were born in the same year (1863) and died in the same year (1914).
• Ruby and sapphire are crystallized aluminium oxide, colored by traces of chromium, iron or titanium.

Isotopes of aluminium

A single stable isotope, aluminium-27. Radioactive aluminium-26 heated up the earliest asteroids and is now used to date rocks and sediments.

• aluminium-26: radioactive, half-life 717,000 years. Its gamma rays map star formation across the Galaxy; paired with beryllium-10, it dates when sediments were buried.
• aluminium-27: 100% of natural aluminium, stable

Common compounds

Corundum (ruby, sapphire) (Al₂O₃)

Related elements

Same family (post-transition metals): Gallium (Ga), Indium (In), Tin (Sn), Thallium (Tl), Lead (Pb), Bismuth (Bi), Polonium (Po).

Same column (group 13): Boron (B), Gallium (Ga), Indium (In), Thallium (Tl), Nihonium (Nh).