Aluminum

Aluminum is the chemical element with atomic number 13 and the symbol Al. It is a soft, silvery-white, lightweight metal in group 13 of the periodic table, and it is the most abundant metal in the Earth’s crust. The International Union of Pure and Applied Chemistry (IUPAC) spells the name aluminium, which is also the usual spelling outside North America.

History of aluminum

The name comes from alumen, the Latin word for alum, a bitter salt used for centuries in dyeing and medicine. By the end of the 1700s chemists suspected that alum and aluminum oxide contained an unknown metal, but every attempt to separate it failed. Humphry Davy had used an electric current to free sodium and potassium from their oxides, yet the same approach did not release aluminum.

The Danish physicist Hans Christian Oersted made the first, impure sample in 1825 by heating aluminum chloride with potassium. The German chemist Friedrich Wöhler improved the method in 1827 and produced the pure metal for the first time, using sodium in place of potassium. The metal remained difficult to make in quantity for decades afterward.

The modern industry began in 1886, when the American Charles Martin Hall and the Frenchman Paul Héroult each developed an electrolytic process, working independently. Their method dissolves aluminum oxide in molten cryolite and passes a current through the mixture. It turned aluminum from a laboratory curiosity into a bulk industrial material.

Properties of aluminum

Aluminum has a standard atomic weight of about 26.98 and an electron configuration of [Ne] 3s2 3p1. The three outer electrons are lost easily, so the element almost always appears with an oxidation state of +3. PubChem lists a first ionization energy of 5.986 electronvolts and an electronegativity of 1.61 on the Pauling scale.

The metal melts at about 660 degrees Celsius and boils at about 2,519 degrees Celsius. Its density is 2.70 grams per cubic centimeter, which is low for a metal that is also strong once alloyed. Aluminum is non-magnetic and does not produce sparks, and it is the second most malleable and the sixth most ductile of all metals.

Fresh aluminum reacts with oxygen in air and quickly forms a thin, tough layer of oxide on its surface. This layer shields the metal underneath, which explains why aluminum resists corrosion far better than its chemical reactivity would suggest. The metal also conducts heat and electricity well. Weight for weight it carries almost twice as much current as copper does.

Occurrence and production of aluminum

Aluminum makes up about 8.1 percent of the Earth’s crust by mass, a larger share than any other metal. It is almost never found as a free metal because it binds so strongly to oxygen. The main commercial ore is bauxite, a mixture of aluminum-rich minerals that forms in tropical regions where rock has weathered for a very long time.

Production takes place in two stages. In the Bayer process, bauxite is dissolved in hot sodium hydroxide solution and refined into pure aluminum oxide, known as alumina. In the Hall-Héroult process, the alumina is dissolved in molten cryolite and split by electrolysis into aluminum metal and oxygen.

Smelting is extremely energy intensive. The Royal Society of Chemistry notes that about 5 percent of the electricity generated in the United States goes into making aluminum. Recycling uses only a small fraction of that energy, and because the metal does not corrode away, recycled aluminum can be melted and reused repeatedly.

Uses of aluminum

Aluminum appears in a huge range of products, including beverage cans, foil, kitchen utensils, window frames, beer kegs and aircraft parts. Pure aluminum is not especially strong, so manufacturers usually combine it with other metals. Alloys with copper, manganese, magnesium and silicon are light but strong, and they are vital in building aircraft and other vehicles. An alloy is a metallic mixture designed to have better properties than any of its parts alone.

Aluminum is also used in electrical transmission lines, where its low cost and low weight outweigh its slightly poorer conductivity per unit of volume. When evaporated in a vacuum, it forms a thin coating that reflects both light and heat. Such coatings are used on telescope mirrors, decorative paper, packaging and toys, and unlike silver they do not tarnish.

Compounds extend the list further. Aluminum oxide is used as an abrasive and as a ceramic, alum is still used in water treatment, and aluminum hydroxide is an ingredient in some indigestion tablets. In construction, aluminum cladding, roofing and structural sections are valued for resisting weather without painting.

Isotopes of aluminum

Aluminum has only one stable isotope, aluminum-27, so natural aluminum is made of that isotope alone. This makes it a monoisotopic element, and its atomic weight is therefore very precise. IUPAC and PubChem list the value as 26.981538.

The best-known radioactive isotope is aluminum-26, which has a half-life of about 717,000 years. It formed in stars and was present in the early solar system. Scientists measure its decay products in meteorites to work out how quickly the first solid bodies formed. An isotope is a version of an element with a specific number of neutrons, and the half-life is the time it takes half of a radioactive sample to decay.

Health and environmental effects of aluminum

Aluminum has no known biological role. In its soluble +3 form it is toxic to many plants, and acidic soils, which cover almost half of the world’s arable land, release more of it from minerals. Crops can then take up the dissolved metal, which reduces their yields.

People absorb only a small amount of the aluminum they eat. Foods with above-average levels include tea, processed cheese, lentils and cakes made with aluminum-based raising agents. The Royal Society of Chemistry states that cooking in aluminum pans does not greatly raise dietary intake, except when acidic foods such as rhubarb are cooked in them.

A link between aluminum in the body and Alzheimer’s disease has been suggested, but it has not been proven. This entry is general background rather than medical advice. Mining and refining also carry environmental costs, including the large amounts of energy used and the alkaline residue left over from alumina production.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue