lĭthˈēəm [Gr.,=stone], metallic chemical element; symbol Li; at. no. 3; at. wt. 6.941; m.p. about 180.54 degrees Celsius; b.p. about 1,342 degrees Celsius; sp. gr. .534 at 20 degrees Celsius; valence +1. Lithium is a soft, silver-white metal. It is one of the alkali metals in group Ia of the periodic table. It is the least dense metal. Because it has high specific heat, it has found some use in cooling systems for nuclear reactors; such use is limited because lithium is very corrosive. Lithium metal is prepared by electrolysis of fused lithium chloride. Lithium reacts with water less readily than sodium. It burns in air with a brilliant white flame. Lithium forms many inorganic compounds, among them a hydride (LiH), a nitride (Li₃N), an oxide (lithia, Li₂O), a hydroxide (LiOH), a carbide (Li₂C₂), a carbonate (Li₂CO₃), and a phosphate (Li₃PO₄). When heated it reacts directly with the halogens to form halides. Lithium aluminum hydride (LiAlH₄) is an important reagent in organic chemistry. Lithium also forms numerous organic compounds. One compound of major importance is lithium stearate, produced by cooking tallow (or other animal fat) with lithium hydroxide; lithium stearate is used to transform oil into lithium-base lubricating greases, which have found extensive use in the automotive industry. Lithium carbonate is used in special glasses and ceramic glazes. Lithium chloride and bromide are used as brazing and welding fluxes; they are also used in air conditioning systems because they are very hygroscopic, i.e., they absorb moisture. Lithium hydroxide is used to increase the capacity of alkaline storage cells. Lithium compounds are used in the nuclear energy industry, in the preparation of plastics and synthetic rubber, and in the synthesis of vitamin A. Lithium is added in small amounts to magnesium, aluminum, or lead-base alloys; it is also used as a degasifier in iron, steel, and copper refining. In addition, lithium is used to scavenge small amounts of oxygen and nitrogen in electronic vacuum tubes. Trace amounts of lithium and its compounds color a flame bright red; they are used in pyrotechnics. Lithium in the salt form has recently come into use as a medical treatment for manic depression. Lithium is widely distributed in nature; it is found in the soil, in plants, in animals, and in the human body. It is also found in the sun. Lithium may be profitably extracted from ores containing as little as 1% lithium (measured as lithium oxide). Some commercially important minerals are lepidolite, petalite, spodumene, and amblygonite. Lithium is also produced from brines such as those in Searles Lake, Calif., and in the Great Salt Lake, Utah. Lithium was discovered in 1817 by J. A. Arfvedson.

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