PeriodicElementTable.com
13Al26.981538
Post-transition metal

Aluminum

Aluminum is a lightweight, silvery post-transition metal that's the most abundant metal in Earth's crust, yet it remained rare and expensive for most of human history because it's never found as a free metal in nature. A thin, tough oxide layer forms naturally on its surface, protecting it from corrosion and making it one of the most widely used metals today.

Group · Period
13 · 3
At room temp
solid
Melts at
933.437 K
Density
2.7 g/cm³
Discovered
Ancient

Uses

Aluminum’s light weight and corrosion resistance make it essential across transportation, from aircraft frames to car parts, where cutting weight improves fuel efficiency and performance. Its natural oxide coating also makes it well suited to packaging, most familiarly as foil and beverage cans, and to construction, where it’s used in window frames, siding, and roofing that need to withstand the weather without rusting.

Because it conducts electricity well relative to its weight, aluminum is also used in power transmission lines over long distances, and its versatility as an alloying metal makes it a component in countless manufactured goods, from kitchenware to electronics housings. Aluminum’s ability to be recycled repeatedly without losing quality has made recycling a major part of its overall supply chain.

History

Aluminum-containing compounds, particularly alum, were used by ancient civilizations, including the Egyptians and Greeks and Romans, as dyeing agents and astringents, long before anyone understood aluminum as a distinct metal. The pure metal itself wasn’t produced until 1825, when Danish chemist Hans Christian Ørsted isolated an impure sample, with German chemist Friedrich Wöhler refining the process soon after. Because extracting it remained so difficult, aluminum stayed rarer and more expensive than precious metals until 1886, when Charles Martin Hall in the United States and Paul Héroult in France independently developed the electrolytic process that finally made it affordable and abundant.

Fun facts

  • Aluminum is the most abundant metal in Earth's crust, making up roughly 8% of it, yet it was once rarer and more valuable than gold before modern extraction methods existed.
  • In 1884, the capstone placed atop the Washington Monument was made of pure aluminum, chosen specifically because the metal was still a rare, prestigious material at the time.
  • Aluminum naturally forms a thin, tough oxide layer on its surface that protects it from further corrosion, which is why it holds up so well outdoors and in food packaging.

Frequently asked questions

If aluminum is so common, why was it once more valuable than gold?

Abundance in the ground isn't the same as being easy to get. Aluminum is never found as a free metal in nature — it's always locked tightly into ore — and extracting it required a difficult, expensive process for most of the 1800s. It wasn't until an efficient electrolytic method was developed in 1886 that aluminum became cheap enough for everyday use.

Is aluminum magnetic?

No, aluminum isn't magnetic in the way iron is — it won't stick to a refrigerator magnet. It is, however, a good electrical conductor, which combined with its light weight is part of why it's used in power transmission lines and electronics.

Why is aluminum recycled so heavily compared to other metals?

Aluminum can be melted down and reused indefinitely without losing its properties, and recycling it takes a small fraction of the energy needed to produce new aluminum from raw ore. That combination makes aluminum recycling both practical and economically worthwhile, which is why cans and scrap aluminum are collected so widely.

Compounds

7 notable compounds containing Al

  • AlCl3industrial

    Aluminum chloride

    A covalent compound in its anhydrous form and a strong Lewis acid, often existing as the dimer Al2Cl6 in the vapor phase.

    Used for: Catalyst in Friedel-Crafts reactions, antiperspirant active ingredient

  • Al(OH)3base

    Aluminum hydroxide

    An amphoteric compound able to react as either an acid or a base, typically forming a gelatinous precipitate when made in water.

    Used for: Antacid medication, flame retardant, water treatment

  • Al2O3oxide

    Aluminum oxide

    An extremely hard, high-melting ionic oxide found naturally as corundum, the mineral behind ruby and sapphire gemstones.

    Used for: Abrasives, refractory ceramics, primary ore for aluminum metal

  • Al2(SO4)3salt

    Aluminum sulfate

    An ionic salt that hydrolyzes in water to give a mildly acidic solution, historically combined with a second sulfate to form alum.

    Used for: Water treatment flocculant, paper sizing, soil pH control

  • Be3Al2Si6O18mineral

    Beryl

    A ring-silicate mineral whose color comes from trace impurities: chromium or vanadium produces emerald, while iron produces aquamarine.

    Used for: Gemstone (emerald, aquamarine), primary ore of beryllium

  • CoAl2O4industrial

    Cobalt blue

    A vividly blue spinel-structured pigment formed by firing cobalt(II) and aluminum oxides together. It has been prized for centuries for its rich, stable color in art and ceramics.

    Used for: Blue pigment in paints, ceramics, and glass

  • Y3Al5O12industrial

    Yttrium aluminum garnet (YAG)

    A synthetic garnet crystal that, when doped with neodymium or other rare-earth ions, forms the gain medium of one of the most widely used solid-state lasers.

    Used for: Host crystal for Nd:YAG lasers; also cut as a diamond-simulant gemstone

Isotopes

23 known isotopes

Swipe to see all columns →

IsotopeNatural abundanceHalf-lifeDecay modeMass excessBinding energy / nucleonDecay width
Al-27 stable 100% Stable — -17,196.86 keV 8,331.55 keV —
Show all 23 isotopes
Al-21 — 35 ns Proton emission 27,090 keV 6,297 keV 1.30 × 10-8 eV
Al-22 — 91.1 ms Electron capture / beta-plus decay (100%), Beta-plus, proton emission (55%), B+2P (1.1%) 18,201 keV 6,782 keV 5.01 × 10-15 eV
Al-23 — 446 ms Electron capture / beta-plus decay (100%), ECP (1.04%) 6,748.07 keV 7,335.73 keV 1.02 × 10-15 eV
Al-24 — 2.053 s Electron capture / beta-plus decay (100%), ECA (0.035%), ECP (0.0016%) -48.81 keV 7,649.58 keV 2.22 × 10-16 eV
Al-25 — 7.183 s Electron capture / beta-plus decay (100%) -8,915.97 keV 8,021.14 keV 6.35 × 10-17 eV
Al-26 — 7.17E+5 Y Electron capture / beta-plus decay (100%) -12,210.14 keV 8,149.77 keV 2.02 × 10-29 eV
Al-28 — 2.245 m Beta-minus decay (100%) -16,850.72 keV 8,309.9 keV 3.39 × 10-18 eV
Al-29 — 6.56 m Beta-minus decay (100%) -18,207.76 keV 8,348.46 keV 1.16 × 10-18 eV
Al-30 — 3.62 s Beta-minus decay (100%) -15,864.12 keV 8,261.1 keV 1.26 × 10-16 eV
Al-31 — 644 ms Beta-minus decay (100%), Beta-minus, neutron emission (1.6%) -14,950.71 keV 8,225.52 keV 7.08 × 10-16 eV
Al-32 — 33.0 ms Beta-minus decay (100%), Beta-minus, neutron emission (0.7%) -11,099.37 keV 8,100.34 keV 1.38 × 10-14 eV
Al-33 — 41.7 ms Beta-minus decay (100%), Beta-minus, neutron emission (8.5%) -8,497.38 keV 8,020.62 keV 1.09 × 10-14 eV
Al-34 — 56.3 ms Beta-minus decay (100%), Beta-minus, neutron emission (26%) -2,997.62 keV 7,860.35 keV 8.10 × 10-15 eV
Al-35 — 38.3 ms Beta-minus decay (100%), Beta-minus, neutron emission (38%), B-2N (0%) -223.73 keV 7,787.12 keV 1.19 × 10-14 eV
Al-36 — 90 ms Beta-minus decay (100%), Beta-minus, neutron emission (31%) 5,950.38 keV 7,623.52 keV 5.07 × 10-15 eV
Al-37 — 10.7 ms Beta-minus decay (100%), Beta-minus, neutron emission 9,809.56 keV 7,531.32 keV 4.26 × 10-14 eV
Al-38 — 9.0 ms Beta-minus, neutron emission, B-2N, Beta-minus decay 16,470 keV 7,370 keV 5.07 × 10-14 eV
Al-39 — 7.6 ms Beta-minus decay (100%), B-2N, Beta-minus, neutron emission 21,490 keV 7,260 keV 6.00 × 10-14 eV
Al-40 — 260 ns Beta-minus decay (100%), B-2N, Beta-minus, neutron emission 28,820 keV 7,097 keV 1.75 × 10-9 eV
Al-41 — — Beta-minus decay (100%), Beta-minus, neutron emission 34,590 keV 6,980 keV —
Al-42 — 170 ns Beta-minus decay, Beta-minus, neutron emission, B-2N 41,990 keV 6,829 keV 2.68 × 10-9 eV
Al-43 — 170 ns Beta-minus decay, Beta-minus, neutron emission, B-2N 48,270 keV 6,712 keV 2.68 × 10-9 eV