Lithium is an extremely soft silvery-gray metallic element, identified by the symbol Li on the periodic table of elements. The metal is used in a range of industries, typically in the form of alloys and compounds, since it is extremely reactive. Consumers may also be familiar with salts of lithium, which are used as mood altering drugs.

The reasonably abundant element was discovered in the early 1800s, although it took the work of several chemists to untangle the complexities of lithium. It has an atomic number of three, making it the lightest solid element, and the head of the alkaline metal group. Like other metals in this group, lithium is very reactive in a pure form, and it needs to be handled carefully. The pure metal is not found in nature, since it combines readily with other elements to form compounds.

The element was originally called lithion, derived from the Greek lithos for “stone. As the name would suggest, lithium is often found in rocks, and the bulk of lithium extraction uses igneous rocks as a source. It does not appear to have an important role biologically, although it may be necessary in the form of a trace element. In larger amounts, lithium can be toxic for humans, especially if it has been allowed to oxidize and form a caustic tarnish. Typically, lithium is stored in oil or another nonreactive material to retard corrosion.

The metal has a very high specific heat, meaning that it melts slowly and will hold high temperatures. It is often used as a heat transfer medium, and it is found in alloys, glass, and ceramics. The light weight of the metal makes it a popular choice in batteries, since it also has a high electrochemical potential, meaning that the metal can store energy. Among many other uses, lithium can act as an air purifier, trapping carbon dioxide in enclosed environments like aircraft and submarines.

Pure lithium is not used pharmacologically. Rather, the salts of the metal are, particularly lithium carbonate, which was approved by the Food and Drug Administration (FDA) in 1970. Salts of the metal appear to be effective in correcting imbalances in the brain which lead to mood disorders. Lithium acts on the neurotransmitters of the brain, and may also be used in the treatment of severe headaches. Since it is potentially dangerous in large amounts, doctors usually monitor blood lithium levels throughout treatment, to ensure that patients stay healthy.