n.
Chemical element , lightest alkali metal , chemical symbol Li, atomic number 3.
It is soft, white, lustrous, and very reactive, forming compounds in which it has valence 1. The metal is used in certain alloys , as a coolant in nuclear reactors, and (because of its reactivity) as a reagent, scavenger, and rocket fuel. Lithium hydride is used as a source of hydrogen; lithium hydroxide is used as an additive in storage batteries and to absorb carbon dioxide. Halides (see halogen ) of lithium are used as moisture absorbents, and lithium soaps are used as thickeners in lubricating greases. Lithium carbonate is an important drug for treating depression and bipolar disorder .