Aluminum (Al)

Aluminium is the most abundant metal in the Earth's crust and was, until the 1880s, more expensive than gold — Napoleon III is said to have reserved aluminium cutlery for his most honoured guests. The Hall-Héroult electrolysis process, invented independently by two 22-year-olds in 1886, collapsed the price by a factor of two hundred within a decade. It resists corrosion not by being unreactive but by being extremely reactive: a fresh surface oxidises within milliseconds into a dense film a few nanometres thick that seals the metal underneath.

Properties

Atomic number

13

Symbol

Al

Standard atomic weight

26.982 u

Category

Post-transition metal

Group

13

Period

3

Block

p-block

Electron configuration

[Ne] 3s² 3p¹

Electrons per shell

2, 8, 3

Melting point

933.44 K — 660.3 °C — 1220.5 °F

Boiling point

2,792 K — 2518.8 °C — 4565.9 °F

Density

2.7 g/cm³

Electronegativity

1.61 (Pauling)

Oxidation states

+3

Discovered

1825 by Hans Christian Ørsted

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p¹

Noble gas shorthand

[Ne] 3s² 3p¹

Shells

K: 2 · L: 8 · M: 3

What it is used for

• Drink cans, foil and food packaging
• Window frames, ladders and curtain walling
• Aircraft skins and airframes
• Overhead power transmission lines, usually over a steel core
• Engine blocks, wheels and heat sinks

Spelled "aluminum" here because US search volume dominates; "aluminium" is the IUPAC spelling and is carried as an alias. Recycling it takes about 5% of the energy of smelting it from ore, which is why used cans have real scrap value.

Neighbours in the table

Group 13

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Aluminum sits in group 13 with boron, gallium, indium, thallium, nihonium.