Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has a great affinity towards oxygen, and forms a protective layer of oxide on the surface when exposed to air. Aluminium visually resembles silver, both in its color and in its great ability to reflect light. It is soft, non-magnetic and ductile. It has one stable isotope, 27Al; this isotope is very common, making aluminium the twelfth most common element in the Universe. The radioactivity of 26Al is used in radiodating.

Aluminium, 13Al
Alternative namealuminum (U.S., Canada)
Appearancesilvery gray metallic
Standard atomic weight Ar, std(Al)26.9815384(3)[1]
Aluminium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson


Atomic number (Z)13
Groupgroup 13 (boron group)
Periodperiod 3
Block  p-block
Electron configuration[Ne] 3s2 3p1
Electrons per shell2, 8, 3
Physical properties
Phase at STPsolid
Melting point933.47 K (660.32 °C, 1220.58 °F)
Boiling point2743 K (2470 °C, 4478 °F)
Density (near r.t.)2.70 g/cm3
when liquid (at m.p.)2.375 g/cm3
Heat of fusion10.71 kJ/mol
Heat of vaporization284 kJ/mol
Molar heat capacity24.20 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1482 1632 1817 2054 2364 2790
Atomic properties
Oxidation states−2, −1, +1,[2] +2,[3] +3 (an amphoteric oxide)
ElectronegativityPauling scale: 1.61
Ionization energies
  • 1st: 577.5 kJ/mol
  • 2nd: 1816.7 kJ/mol
  • 3rd: 2744.8 kJ/mol
  • (more)
Atomic radiusempirical: 143 pm
Covalent radius121±4 pm
Van der Waals radius184 pm
Color lines in a spectral range
Spectral lines of aluminium
Other properties
Natural occurrenceprimordial
Crystal structure face-centered cubic (fcc)
Speed of sound thin rod(rolled) 5000 m/s (at r.t.)
Thermal expansion23.1 µm/(m⋅K) (at 25 °C)
Thermal conductivity237 W/(m⋅K)
Electrical resistivity26.5 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[4]
Molar magnetic susceptibility+16.5×10−6 cm3/mol
Young's modulus70 GPa
Shear modulus26 GPa
Bulk modulus76 GPa
Poisson ratio0.35
Mohs hardness2.75
Vickers hardness160–350 MPa
Brinell hardness160–550 MPa
CAS Number7429-90-5
Namingfrom alumine, obsolete name for alumina
PredictionAntoine Lavoisier (1782)
DiscoveryHans Christian Ørsted (1824)
Named byHumphry Davy (1812[lower-alpha 1])
Main isotopes of aluminium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
26Al trace 7.17×105 y β+ 26Mg
ε 26Mg
27Al 100% stable
 Category: Aluminium
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Chemically, aluminium is a weak metal in the boron group; as is common for the group, aluminium forms compounds primarily in the +3 oxidation state. The aluminium cation Al3+ is small and highly charged; as such, it is polarizing, and bonds aluminium forms tend towards covalency. The strong affinity towards oxygen leads to aluminium's common association with oxygen in nature in the form of oxides; for this reason, aluminium is found on Earth primarily in rocks in the crust, where it is the third most abundant element after oxygen and silicon, rather than in the mantle, and virtually never as the free metal.

The discovery of aluminium was announced in 1825 by Danish physicist Hans Christian Ørsted. The first industrial production of aluminium was initiated by French chemist Henri Étienne Sainte-Claire Deville in 1856. Aluminium became much more available to the public with the Hall–Héroult process developed independently by French engineer Paul Héroult and American engineer Charles Martin Hall in 1886, and the mass production of aluminium led to its extensive use in industry and everyday life. In World Wars I and II, aluminium was a crucial strategic resource for aviation. In 1954, aluminium became the most produced non-ferrous metal, surpassing copper. In the 21st century, most aluminium was consumed in transportation, engineering, construction, and packaging in the United States, Western Europe, and Japan.

Despite its prevalence in the environment, no living organism is known to use aluminium salts metabolically, but aluminium is well tolerated by plants and animals. Because of the abundance of these salts, the potential for a biological role for them is of continuing interest, and studies continue.