Average mass of an atom in unified atomic mass units (1 u is 1/12 of the mass of a carbon-12 atom). Accounts for the natural mix of the element’s isotopes.
Number of the vertical column, 1 to 18 in IUPAC numbering. Elements in a group share the same outer-shell layout, so their properties are alike.
Number of the horizontal row. Usually equal to the number of electron shells in the atom; palladium is the exception, with four shells in period 5.
The subshell (s, p, d or f) that receives the last electrons in the usual filling order; it divides the table into four blocks. Real atoms sometimes differ: lanthanum starts the f-block but has no f electrons.
[Ne] 3s² 3p¹
How electrons are arranged in subshells. The bracket stands for the previous noble gas; the superscript is the number of electrons in a subshell.
2, 8, 3
Number of electrons in each shell, from the nucleus outwards.
660.3 °C (933.44 K)
Temperature at which the solid turns liquid at standard pressure. Helium, carbon and arsenic do not melt at normal pressure: helium needs about 25 atm, carbon and arsenic turn straight into vapour.
2,519 °C (2,792 K)
Temperature at which the liquid boils at standard pressure. For carbon and arsenic, the temperature at which the solid turns straight into vapour (sublimation).
2.7 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
1.61 Pauling
How strongly an atom pulls electrons towards itself in a chemical bond. On the Pauling scale it runs from 0.79 for caesium to 3.98 for fluorine.
5.986 eV
Energy needed to remove the most loosely bound electron from an atom. The lower it is, the more easily the element gives up an electron, which is typical of metals.
0.433 eV
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
121 pm
Half the length of a single covalent bond between two atoms of the element. It shows the size of an atom inside a molecule or crystal: 76 pm for carbon, 132 pm for iron.
+3
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Aluminium (Al) is a chemical element with atomic number 13. It sits in group 13 and period 3 of the periodic table, in the p-block. It is a post-transition metal. At room temperature it is a solid. Its standard atomic weight is 26.982.
Origin of the name
The name comes from alum, Latin alumen, a salt that the Greeks and Romans used to fix dyes and to stop bleeding. Humphry Davy first proposed alumium, then aluminum; the form aluminium, with the usual -ium ending, won in Britain and in chemistry, while Americans kept aluminum.
Where is aluminium found?
Aluminium is the most abundant metal in the Earth’s crust and the third most abundant element, about 8%, after oxygen and silicon. It never occurs free: it is bound in clays, feldspars and many other minerals. The ore it is made from is bauxite, and ruby and sapphire are crystals of aluminium oxide coloured by traces of other metals.
What is aluminium used for?
Light and resistant to corrosion, aluminium is everywhere: drink cans, foil, cookware, window frames, aircraft and rockets. Power lines are made of it because it is much lighter than copper. Pure aluminium is soft, so it is usually alloyed with copper, magnesium or silicon. A thin layer of aluminium makes the mirrors of telescopes.
Interesting facts
In the mid-19th century aluminium was more precious than gold; it became cheap only after 1886, when Charles Martin Hall and Paul Héroult found how to make it by electrolysis.
In air aluminium is instantly covered with a thin film of oxide, which protects it from further corrosion.
Although aluminium is everywhere in soil and water, no living thing is known to use it.