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.
Aluminum has 13 electrons, one for every proton, so the atom carries no charge. Below are the same 13 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p¹
Short form: [Ne] 3s² 3p¹, where [Ne] stands for the 10 electrons neon already has.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 2 here is 2s² 2p⁶, and 2 + 6 is 8.
Aluminum sits in period 3 and has 3 shells. The period number counts the shells.
The outer shell holds 3 electrons. Those are the ones aluminum can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 13 means 3.
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.