ChemSphere
13Al26.982

Aluminium

Post-transition metal · Period 3 · Group 13 · p-block

Once costlier than silver, now wrapped around everything

Atomic mass
26.982 u
State at 25 °C
Solid
Electronegativity
1.61
Melting point
660.3 °C
Boiling point
2,469.9 °C
Configuration
[Ne] 3s2 3p1
Building atom…
13 protons 14 neutrons 13 electrons

Aluminium, explained

Overview

Aluminium ([Ne]3s2 3p1) readily gives up three electrons to form Al3+, and its standard electrode potential (-1.66 V) marks it as a reactive metal. Yet aluminium objects last for decades because the surface instantly grows a transparent layer of aluminium oxide only a few nanometres thick, which seals the metal from air and water. The small, highly charged Al3+ ion makes aluminium amphoteric: the metal and its oxide dissolve in both acids and strong bases, releasing hydrogen in the latter case.

Aluminium is the most abundant metal in Earth's crust, about 8% by mass, but it is locked in very stable compounds, so extracting it takes a great deal of energy. Bauxite ore is refined into alumina by the Bayer process, and the alumina is dissolved in molten cryolite and split by electrolysis in the Hall-Héroult process. Recycling skips this step and uses only about 5% of the energy. With a density of 2.70 g/cm3, about a third that of steel, aluminium is used in aircraft, cans, cables and buildings.

Discovery

Hans Christian Ørsted produced impure aluminium in 1825 by reducing aluminium chloride with potassium amalgam, and Friedrich Wöhler improved the method in 1827. When Henri Sainte-Claire Deville developed sodium reduction in 1854, the metal was still rarer than silver. In 1886 Charles Martin Hall in the United States and Paul Héroult in France independently invented electrolytic production, making it cheap. Humphry Davy named it after alum (Latin alumen); 'aluminium' is the IUPAC spelling, 'aluminum' the American one.

Where it’s found
Aluminium is never found as a native metal; it is mined as bauxite, mainly in Australia, Guinea and China, refined to alumina and smelted electrolytically.
What it’s used for
  • Beverage cans
  • Aircraft structures
  • Power transmission lines
  • Window frames
  • Kitchen foil
  • Water treatment
In living things
Aluminium has no known biological role. It is poorly absorbed and normally excreted by the kidneys, but it can accumulate to toxic levels in people with kidney failure, and dissolved Al3+ in acidic soils damages plant roots.
Safety
Bulk aluminium is safe, but fine aluminium powder is flammable and can form explosive dust clouds. Molten aluminium contacting water can cause violent steam explosions.

How it compares

Where Aluminium sits among all 118 elements on the trends that shape the table.

  • Electronegativity1.61Pauling

    #50 of 100 elements with data

  • Ionization energy578kJ/mol

    #81 of 104 elements with data

  • Atomic radius125pm

    #75 of 95 elements with data

  • Electron affinity41.8kJ/mol

    #59 of 109 elements with data

  • Density2.7g/cm³

    #88 of 114 elements with data

  • Melting point933K

    #66 of 110 elements with data

Density
2.7 g/cm³
Atomic radius
125 pm
Covalent radius
126 pm
Molar heat
24.2 J/(mol·K)
Appearance
silvery gray metallic
Discovered by
—

Inside the atom

13 electrons arranged in 3 shells: 2 · 8 · 3.

Orbital diagram

1s2 2s2 2p6 3s2 3p1 · shorthand [Ne] 3s2 3p1

  1. 1s2
  2. 2s2
  3. 2p6
  4. 3s2
  5. 3p1

Each box is an orbital holding up to two electrons of opposite spin. Highlighted subshells hold the valence electrons that decide how Aluminium bonds.

Ionization energies

Energy to remove each electron in turn, on a log scale. The biggest leap, from electron 11 to 12 (×4.7), is where the next electron has to come from a filled shell much closer to the nucleus.

Signature reactions

The chemistry Aluminium is known for.

  1. Redox · Single displacement

    Thermite reaction

    Powdered aluminium reduces iron oxide in a shower of sparks, reaching about 2500 °C and producing molten iron. The reaction is used to weld railway tracks in the field. It works because aluminium oxide is far more stable than iron oxide.

    2Al(s)+Fe2O3(s)Al2O3(s)+2Fe(l)

    Conditions: ignition with a magnesium fuse

  2. Redox · Electrolysis

    Hall-Héroult electrolysis

    Alumina dissolved in molten cryolite is electrolysed; aluminium collects as a liquid at the cathode while oxygen reacts with the carbon anodes to form CO2. Smelters consume roughly 13-15 kWh of electricity per kilogram of aluminium. That is why they are often built near cheap hydroelectric power.

    2Al2O3(l)+3C(s)4Al(l)+3CO2(g)

    Conditions: about 960 °C, alumina dissolved in molten cryolite

  3. Redox · Amphoteric

    Aluminium dissolving in alkali

    Sodium hydroxide dissolves the protective oxide film and then the metal itself, releasing bubbles of hydrogen and forming soluble aluminate. This reaction is why aluminium cookware should not be cleaned with strong alkaline cleaners. Some drain cleaners use it to generate heat and gas that loosen clogs.

    2Al(s)+2NaOH(aq)+6H2O(l)2Na[Al(OH)4](aq)+3H2(g)

    Conditions: room temperature, concentrated NaOH

Watch Aluminium react in 3D

Where you’ll meet it

  • Aluminum can

    Aluminum can

    Hundreds of billions of aluminium drink cans are made each year, and most are recyclable indefinitely.

    Photo: Wikimedia Commons
  • Boeing 747

    Boeing 747

    Like most airliners, the 747's airframe is built mainly from aluminium alloys.

    Photo: Wikimedia Commons
  • Bauxite

    Bauxite

    This reddish ore of aluminium hydroxides and oxides is the starting point for nearly all aluminium.

    Photo: Wikimedia Commons
  • Washington Monument

    Washington Monument

    The monument's tip is a small aluminium pyramid installed in 1884.

    Photo: Wikimedia Commons

Research

No research on Aluminium yet

When Bhavya publishes a project that studies Aluminium, it will be linked here.

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