Al · Element 13 · Boron group
Once more precious than gold, now the most-used metal after iron — because someone worked out how to electrolyse it cheaply.
Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where aluminum sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Size, to scale
Radius 143 pm — that is 0.143 nm, so about 3497 million of them side by side would span a millimetre.
Thermal range
Aluminum is liquid over a 1859 K window, from 933 K to 2792 K.
The story
Aluminum is the miracle metal that went from precious to everywhere in just 100 years. Once more valuable than gold (Napoleon III served his most honored guests with aluminum cutlery while lesser guests got gold), this lightweight metal is now so common we throw it away. The Washington Monument is capped with aluminum - in 1884, it was the most expensive metal on Earth. The Hall-Héroult process changed everything in 1886, making aluminum extraction affordable and launching the aviation age. Planes fly because aluminum is strong yet weighs one-third as much as steel. Your antiperspirant contains aluminum to block sweat glands, while aluminum foil in your kitchen reflects 95% of infrared radiation. Recycling aluminum uses just 5% of the energy needed to make new aluminum, making that soda can infinitely recyclable.
Aluminum's discovery story spans over two millennia, from ancient civilizations to 19th-century chemical breakthroughs. This tale involves brilliant minds, industrial espionage, and the transformation of the "metal of kings" into everyday material.
The story begins in ancient Rome around 400 BCE, where the word "alumen" described astringent salts used for dyeing and tanning. Roman naturalist Pliny the Elder (23-79 CE) documented alum's properties in his encyclopedia "Naturalis Historia," unknowingly describing aluminum compounds that had been used for centuries.
In 1761, French chemist Louis-Bernard Guyton de Morveau proposed that alum contained a then-unknown metal, coining the term "alumine" for what we now call aluminum oxide. This set the stage for the metal's eventual isolation.
British chemist Sir Humphry Davy (1778-1829) first attempted to isolate aluminum through electrolysis in 1807. Using his newly invented electric battery, Davy successfully isolated potassium and sodium but struggled with aluminum oxide's high melting point (2,072°C). Although unsuccessful in isolating pure aluminum, Davy named the hypothetical metal "aluminum" in 1812, later changed to "aluminium" to match other element names ending in "-ium."
Danish physicist and chemist Hans Christian Ørsted (1777-1851) achieved the first aluminum isolation on August 29, 1825. Using potassium amalgam to reduce aluminum chloride, Ørsted produced tiny metallic globules. His method involved heating aluminum chloride with potassium in a closed tube, creating the first known samples of metallic aluminum.
German chemist Friedrich Wöhler (1800-1882) improved Ørsted's method, using metallic potassium instead of amalgam. On July 21, 1827, Wöhler produced aluminum powder and small beads, becoming the first to observe aluminum's key properties: lightness, resistance to oxidation, and metallic luster. He famously described aluminum as having "the color and luster of tin."
French chemist Henri Étienne Sainte-Claire Deville (1818-1881) revolutionized aluminum production in 1854. His chemical reduction method using sodium made aluminum commercially viable for the first time. Emperor Napoleon III of France funded Deville's research, envisioning aluminum armor and equipment for his army.
During this era, aluminum was more valuable than gold. Napoleon III showcased aluminum cutlery at state dinners, reserving it for the most honored guests while others used gold utensils. The Washington Monument's capstone, completed in 1884, was made of 100 ounces of aluminum - then worth a laborer's annual salary.
Two brilliant young chemists independently discovered the electrolytic process that democratized aluminum:
Age 22, working in his family's woodshed in Oberlin, Ohio, Hall discovered aluminum electrolysis on February 23, 1886. Using his sister Julia's iron skillets and a homemade electric battery, Hall dissolved aluminum oxide in molten cryolite and passed electric current through it, producing pure aluminum droplets.
Also age 22, Héroult made the same discovery just two months later on April 9, 1886. Working in his father's tannery in Gentilly, France, Héroult independently developed the identical process. Both men were born in 1863 and died in 1914 - a remarkable coincidence in scientific history.
The Hall-Héroult process reduced aluminum's price from $545 per pound (1850s) to $0.68 per pound (1900) - a 99.8% price reduction. This breakthrough launched the modern aluminum industry:
Today's aluminum industry produces over 65 million tons annually, enabling modern aviation, space exploration, and sustainable packaging. The Hall-Héroult process, essentially unchanged since 1886, remains the foundation of aluminum production worldwide - a testament to the brilliance of two 22-year-old chemists who transformed civilization.
Applications
Aluminum's unique combination of lightness, strength, and corrosion resistance makes it central across multiple industries. With a density of only 2.7 g/cm³ - about one-third that of steel - aluminum has revolutionized transportation and construction.
The aerospace industry consumes nearly 20% of global aluminum production. Aircraft frames utilize aluminum alloy 2024 (Al-Cu-Mg) for fuselage construction, offering exceptional strength-to-weight ratios. The Boeing 787 Dreamliner contains over 20% aluminum by weight, while modern fighter jets like the F-35 Lightning II use advanced aluminum-lithium alloys that are 10% lighter and 15% stiffer than conventional aluminum alloys.
Modern vehicles incorporate aluminum in engine blocks, transmission cases, and body panels. The Ford F-150 (2015+) features an all-aluminum body that reduced weight by 700 pounds, improving fuel efficiency by 20%. Tesla Model S uses aluminum space frame construction, with 6061-T6 aluminum alloy providing optimal crash protection while maintaining structural integrity.
Architectural aluminum applications include curtain walls, window frames, and roofing systems. The anodization process creates a protective oxide layer up to 25 micrometers thick, offering superior weather resistance. Dubai's Burj Khalifa uses over 1,500 tons of aluminum in its facade system, while the Sydney Opera House's distinctive shells are clad in chevron-patterned aluminum tiles.
Aluminum's electrical conductivity (37.7 MS/m) makes it ideal for power transmission. Aluminum Conductor Steel Reinforced (ACSR) cables carry electricity across continents, with the aluminum providing conductivity while steel core adds tensile strength. High-voltage transmission lines use aluminum because its lighter weight requires fewer support towers compared to copper.
Electronic devices leverage aluminum's thermal conductivity (205 W/m·K) for heat dissipation. MacBook enclosures are machined from single aluminum billets using CNC milling, while smartphone frames use aluminum alloy 6013 for electromagnetic shielding. LED heat sinks utilize aluminum's thermal properties to prevent overheating and extend component lifespan.
Aluminum touches our daily lives in countless ways, often invisible but always essential. From the moment we wake up until we go to sleep, aluminum products surround us.
Americans consume about 54 billion aluminum cans annually - that's roughly 170 cans per person. If these cans were laid end-to-end, they would circle the Earth over 160 times.
Where it comes from
82300 mg/kg of Earth's crust · more abundant than 98% of elements
Aluminum is the third most abundant element in Earth's crust, comprising approximately 8.23% by weight - making it more common than iron. Despite this abundance, aluminum never occurs in pure metallic form in nature due to its high reactivity.
Bauxite contains 45-60% aluminum oxide (Al₂O₃) and is the world's primary aluminum source. Major deposits exist in:
The most abundant aluminum-bearing minerals in Earth's crust, including:
Secondary aluminum minerals formed by weathering:
Aluminum's cosmic journey began in the hearts of massive stars through stellar nucleosynthesis. During a star's lifetime, silicon burning processes create aluminum-26 (²⁶Al), a radioactive isotope with a 720,000-year half-life. When these stars explode as supernovae, they scatter aluminum throughout the galaxy.
Our solar system contains aluminum from multiple stellar generations. Meteorites, particularly carbonaceous chondrites, preserve pristine aluminum compounds from the solar nebula 4.6 billion years ago. The Allende meteorite (fallen 1969) contains aluminum-rich inclusions called CAIs (Calcium-Aluminum-rich Inclusions) - the oldest known materials in our solar system.
While aluminum comprises 8% of Earth's crust, it plays no known essential biological role. However, it significantly impacts plant growth in acidic soils where Al³⁺ ions become soluble and toxic to root systems. Some plants, like tea (Camellia sinensis) and certain ferns, have evolved aluminum tolerance mechanisms, actually accumulating the metal in their tissues.
Precambrian Era (3.8-0.54 billion years ago): Initial aluminum concentration in Earth's crust through differentiation and volcanic activity.
Paleozoic-Mesozoic (540-66 million years ago): Formation of major bauxite deposits through tropical weathering of aluminum-rich rocks.
Cenozoic Era (66 million years ago-present): Continued bauxite formation in tropical regions, with Australia's deposits forming 35-55 million years ago.
Handling
While aluminum is generally considered safe for everyday use, proper handling and awareness of potential hazards are essential, especially in industrial settings and for individuals with specific sensitivities.
OSHA PEL: 15 mg/m³ (total dust), 5 mg/m³ (respirable fraction)
Risk: Aluminum dust inhalation can cause pulmonary fibrosis ("aluminum lung") in industrial workers. Welding aluminum releases aluminum oxide fumes that may cause metal fume fever.
Symptoms: Coughing, shortness of breath, chest tightness, flu-like symptoms
Research Status: Limited evidence suggests high aluminum exposure may contribute to neurological disorders
Populations at Risk: Individuals with kidney disease who cannot effectively excrete aluminum
Precaution: Avoid using aluminum cookware with acidic foods (tomatoes, citrus) which increase aluminum leaching
Irritation Potential: Minimal risk from solid aluminum; aluminum salts may cause skin irritation
Allergic Reactions: Rare but documented cases of aluminum allergy, especially from antiperspirants
Symptoms: Redness, itching, contact dermatitis in sensitive individuals
Aluminum Powder: Fine aluminum dust is highly combustible and explosive
Ignition Sources: Static electricity, sparks, heat sources above 760°C
Fire Suppression: Use dry powder extinguishers; NEVER use water on aluminum fires
Storage: Keep powder in sealed, grounded containers away from oxidizers
Flush immediately with clean water for 15 minutes. Remove contact lenses if easily removable. Seek medical attention if irritation persists.
Wash affected area with soap and water. Remove contaminated clothing. For cuts from aluminum, clean wound and apply antiseptic.
Move to fresh air immediately. If breathing difficulties occur, administer oxygen and seek immediate medical attention.
Rinse mouth with water. Do NOT induce vomiting. Seek medical attention if large amounts consumed or symptoms develop.
• Aluminum is generally safe for consumer products when used as intended
• Industrial workers should follow all OSHA guidelines and company safety protocols
• Individuals with kidney disease should consult physicians about aluminum exposure
• Always read product safety data sheets (SDS) for specific aluminum compounds
Quick answers
Aluminum (symbol Al) is element 13 on the periodic table, a post-transition metal in period 3, group 13. Once more precious than gold, now the most-used metal after iron — because someone worked out how to electrolyse it cheaply. At room temperature it is a solid.
[Ne] 3s² 3p¹, giving 3 occupied shells holding 2, 8, 3 electrons respectively. Its outer shell holds 3 electrons, which is what sets its bonding behaviour.Aluminum melts at 933.5 K (660.3 °C) and boils at 2792 K (2518.9 °C).
The standard atomic weight of Aluminum is 26.982 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.
Aluminum has a density of 2.7 g/cm³. Water is 1.0 g/cm³, so a block of aluminum is about 2.7× heavier.
Aluminum has a Pauling electronegativity of 1.61. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). Values in this middle band tend to form covalent rather than strongly ionic bonds.
Aluminum was discovered in 1825 by Hans Christian Orsted. It is named after latin alumen, "alum".
Aluminum makes up about 8.23% of the Earth's crust — one of the most abundant elements there is.