Lithium is a soft, silver-white metal that belongs to the alkali metal set of chemical elements. It is represented by the symbol Li, and it has the atomic number three. Under normal 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 petroleum.
Lithium salts were used through the 19th century to treat gout. Lithium salts such as lithium carbonate, lithium citrate, and lithium orotate are mood stabilizers. They are used in the action of bipolar disorder since, unlike most other mood altering drugs, they counteract both mania and depression. Lithium can also be used to augment antidepressants.
Because of its specific heat ability, the uppermost of all solids, lithium is often used in heat transfer applications. In the later years of the 20th century lithium became vital as an anode material. Used in lithium-ion batteries because of its high electrochemical potential, a typical cell can produce approximately 3 volts, compared with 1.5 volts for lead/acid or zinc cells.