Lithium ( ) is the chemical element with atomic number 3, and is represented by the symbol Li. It is a soft alkali metal with a silver-white colour. Under standard conditions, it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly reactive, corroding quickly in moist air to form a black tarnish. For this reason, lithium metal is typically stored under the cover of oil. When cut open, lithium exhibits a metallic lustre, but contact with oxygen quickly turns it back to a dull silvery grey color. Lithium is also highly flammable.

According to theory, lithium was one of the very few elements synthesized in the Big Bang; its abundance is now vastly less than that predicted by theory; the processes by which new lithium is created and destroyed, and the true value of its abundance continue to be active matters of study in astronomy. Though very light in atomic weight lithium is less common in the universe than any of the first 20 elements due to its low nuclear binding energy.

Due to its high reactivity it only appears naturally on Earth in the form of compounds. Lithium occurs in a number of pegmatitic minerals, but is also commonly obtained from brines and clays; on a commercial scale, lithium metal is isolated electrolytically from a mixture of lithium chloride and potassium chloride.

Trace amounts of lithium are present in the oceans and in some organisms, though the element serves no apparent biological function in humans. Nevertheless, the neurological effect of the lithium ion Li⁺ makes some lithium salts useful as a class of mood stabilizing drugs. Lithium and its compounds have several other commercial applications, including heat-resistant glass and ceramics, high strength-to-weight alloys used in aircraft, and lithium batteries. Lithium also has important links to nuclear physics: the splitting of lithium atoms was the first man-made form of a nuclear reaction, and lithium deuteride serves as the fusion fuel in staged thermonuclear weapons.

History and etymology

Petalite (lithium aluminium silicate) was first discovered in 1800 by the Luso-Brazilian scientist José Bonifácio de Andrade e Silva, who discovered the mineral in a Swedish iron mine on the island of Utö. However, it was not until 1817 that Johan August Arfwedson, then a trainee in the laboratory of Jöns Jakob Berzelius, discovered the presence of a new element while analyzing petalite ore. The element formed compounds similar to those of sodium and potassium, though its carbonate and hydroxide were less water soluble and had a larger capacity to neutralize acid. Berzelius gave the alkaline material the name "lithos", from the Greek λιθoς (lithos, "stone"), to reflect its discovery in a mineral, as opposed to sodium and potassium which had been discovered in plant tissue; its name would later be standardized as "lithium". Arfwedson later showed that this same element was present in the mineral ores spodumene and lepidolite. In 1818, Christian Gmelin was the first to observe that lithium salts give a bright red color in flame. However, both Arfwedson and Gmelin tried and failed to isolate the element from its salts. The element was not isolated until 1821, when William Thomas Brande performed electrolysis on lithium oxide, a process which had previously been employed by Sir Humphry Davy to isolate potassium and sodium. Brande also described pure salts of lithium, such as the chloride, and performed an estimate of its atomic weight. In 1855, Robert Bunsen and Augustus Matthiessen produced large quantities of the metal by electrolysis of lithium chloride. Commercial production of lithium metal began in 1923 by the German company Metallgesellschaft AG through the electrolysis of a molten mixture of lithium chloride and potassium chloride.