Lithium, a silvery-white metallic chemical element. Lithium is the lightest metal and the third lightest of all elements. (Only hydrogen and helium, both gases, are lighter.) Lithium is softer than lead and is ductile (capable of being drawn into wire). It is a good conductor of electricity, and can combine with many other metals to form alloys. When exposed to air, lithium tarnishes rapidly. It is therefore stored under gasoline or kerosene, or in airtight containers. At high temperatures, lithium is capable of absorbing gases.

Lithium is used to remove oxygen and other gases in the manufacture of stainless steels, copper, and copper alloys. The addition of a small percentage of lithium increases the strength of aluminum alloys, lead, and tin. Lithium-magnesium alloys have numerous industrial and structural uses. Lithium is irradiated with neutrons to produce tritium, a radioactive isotope of hydrogen widely used in medicine.

Lithium forms many useful compounds. Lithium stearate is used as a thickener for all-purpose lubricating greases. Lithium bromide and lithium chloride readily absorb moisture and are used in air conditioners and dry cell batteries. Lithium carbonate is used in treating manic-depressive illnesses. Other lithium compounds are used as fluxes (substances that combine with impurities) in welding and brazing, and in the manufacture of ceramics, glass, porcelain enamels, and bleaches.

The element was discovered in 1817 by the Swedish chemist Johan A. Arfvedson. It is widely distributed in the earth's crust, and is always found combined with other elements in various minerals. The chief ores of lithium are spodumene and petalite, two minerals composed of lithium, aluminum, silicon, and oxygen; and amblygonite, a mineral composed of lithium, aluminum, fluorine, phosphorus, and oxygen. Lithium compounds are obtained from the ores by various chemical processes. The metal is usually obtained by electrolysis of lithium chloride.

Symbol: Li. Atomic number: 3. Atomic weight: 6.941. Melting point: 356 F. (180 C). Boiling point: 2,457 F. (1,347 C). Specific gravity: 0.53. Lithium has two stable isotopes: Li-6 and Li-7. It belongs to Group I-A of the Periodic Table and has a valence of + 1.