The lightest metal
Lithium is a silvery-white metal soft enough to cut with a knife and so light that it floats on oil: at 0.534 g/cm³ it is the least dense solid element. Its atom has a single electron outside a helium core, and like the other alkali metals it gives that electron up easily, with the most negative electrode potential of any element. It is nevertheless the mildest of the family: it tarnishes in air, reacts with waterCompound: Water. Two hydrogens, one oxygen, and most of the living world steadily rather than explosively, and is the only alkali metal that combines with nitrogen at room temperature, to form the nitride Li₃N.
It has two stable isotopes, ⁷Li and, about one atom in thirteen, ⁶Li. Lithium-7 is the only nuclide beyond helium made in quantity in the Big Bang, yet lithium is far scarcer in the universe than helium or carbon: stars burn it faster than they make it.
Where it is found and how it is made
About 20 parts per million of the Earth's crust is lithium, never as the metal. It sits in a few minerals — spodumene, petalite and lepidolite, in the coarse granites called pegmatites — and, dissolved as the chloride, in the brines under the salt flats of the Andes: the Salar de Atacama in Chile, the Salar de Uyuni in Bolivia and the salars of Argentina, the so-called lithium triangle. Australia mines the most, from spodumene at Greenbushes; Chile and China pump and evaporate the brines.
Almost all lithium is used as a compound, the carbonate or the hydroxide. The metal itself is made as Bunsen made it in 1855, by electrolysis of molten lithium chloride, mixed with potassium chloride to bring its melting point down to about 450 °C, and is stored under oil or argon.
Batteries and moods
Because it is the lightest metal and gives up its electron most readily, lithium stores more electrical energy for its weight than any other. Stanley Whittingham built the first rechargeable lithium cell in the 1970s; John Goodenough found the cobalt oxide cathode in 1980; Akira Yoshino made the anode of carbon and produced a safe cell in 1985, which Sony sold from 1991. The three shared the Nobel Prize in Chemistry in 2019, and their battery, now by far the largest use of lithium, runs phones, laptops and electric cars.
The oldest use is medical. In 1949 the Australian psychiatrist John Cade reported that lithium salts calmed patients in mania, and lithium carbonate remains a standard treatment for bipolar disorder. Lithium also toughens glass and ceramics, lightens aluminium alloys for aircraft, thickens lubricating greases and, as the hydroxide, scrubs carbon dioxide from the air of submarines and spacecraft. Lithium-6 is the source of tritium, and lithium deuteride is the fuel of the hydrogen bomb.
Discovery and name
In 1800 the Brazilian mineralogist José Bonifácio de Andrada e Silva described two new minerals from the iron mine on the Swedish island of Utö: petalite and spodumene. In 1817 Johan August Arfwedson, a young chemist in Jöns Jacob Berzelius's laboratory, analysed petalite and could not make the figures add up. The missing few per cent turned out to be a new alkali, lighter than soda and potash and less soluble in water; he found it in spodumene and lepidolite too. Berzelius suggested the name lithion, from the Greek lithos, stone, because, unlike sodium and potassium, this alkali had been found in the mineral kingdom rather than in the ashes of plants.
Arfwedson could not free the metal. William Brande obtained specks of it by electrolysis in 1821, and Robert Bunsen and Augustus Matthiessen made it in quantity in 1855 by passing a current through molten lithium chloride.