Lithium is a soft, silver-white metal with symbol "Li" and atomic number 3.
It belongs to the alkali metal group of chemical
elements. Under standard conditions it is the lightest metal and the least
dense solid element. Like all alkali metals, lithium is highly reactive and
flammable. For this reason, it is typically stored in mineral oil.
When cut open, lithium exhibits a metallic luster, but contact with moist air corrodes the surface quickly to a dull silvery
gray, then black tarnish. Because of its high reactivity, lithium never occurs freely in
nature, and instead, only appears in compounds,
which are usually ionic.
Lithium occurs in a number of pegmatitic minerals, but due to its solubility as
an ion is present in ocean water and is commonly obtained from brines and clays. On a commercial
scale, lithium is isolated electrolytically from a mixture of lithium chloride and potassium chloride.
The nuclei of lithium verge on instability, since
the two stable lithium isotopes found in nature have among the lowest binding energies per nucleon of all stable nuclides. Because of its
relative nuclear instability, lithium is less common in the solar system than
25 of the first 32 chemical elements even though the nuclei are very light in
atomic weight. For related reasons, lithium has
important links to nuclear physics.
The transmutation of lithium atoms to helium in 1932 was the first fully man-made nuclear reaction,
and lithium-6
deuteride serves as a fusion fuel in staged thermonuclear weapons.
Lithium and its compounds have several industrial applications, including
heat-resistant glass and ceramics, high
strength-to-weight alloys used in aircraft, lithium
batteries and lithium-ion batteries. These uses consume
more than half of lithium production.
Trace amounts of lithium are present in all organisms. The element
serves no apparent vital biological function, since animals and plants survive
in good health without it. Nonvital functions have not been ruled out. The
lithium ion Li+ administered as any of several lithium salts has proved to be useful as a mood-stabilizing drug in the treatment of bipolar disorder,
due to neurological effects of
the ion in the human body.
