All practice pages/Interatomic theory/Elements
Element 13, a post-transition metal
The most abundant metal in the Earth's crust, once so hard to extract that it was a precious metal, and now cheap enough to wrap sandwiches in.
Period 3, group 13. The other post-transition metals are tinted, and every cell opens its own article.
Three valence electrons, which aluminum gives up to form the Al³⁺ ion. A thin film of aluminum oxide forms on the metal the moment it meets air and protects it from further corrosion.
About 8% of the crust by mass, the most abundant metal there, but always bound to oxygen in clays, feldspars and other minerals. It is mined as bauxite, a soft reddish ore rich in aluminum oxide, mainly in Australia, Guinea and China.
Hans Christian Ørsted produced a small, impure amount in 1825 and Friedrich Wöhler a purer sample in 1827. For decades the metal was a luxury; a small aluminum pyramid was set atop the Washington Monument in 1884 as a showpiece. In 1886 Charles Martin Hall in the United States and Paul Héroult in France independently found how to extract it cheaply with electricity. The name comes from alum, a salt used since ancient times.
Drink cans, foil and food packaging; aircraft, car and train bodies; window frames; and overhead power lines, where it carries electricity at a fraction of copper's weight. Aluminum can be recycled again and again using about 5% of the energy needed to make it new.