LITHIUM

Lithium is a SOFT, silver-white metal that belongs to the alkali metal group of CHEMICAL elements. It is represented by the symbol Li, and it has the atomic number 3. 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, lithium metal is typically STORED in a petroleum derivative, such as mineral oil (in which it floats), or petroleum jelly in which it is held below the surface by the viscosity of the medium. 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. The NUCLEI of lithium are relatively FRAGILE:  the two STABLE lithium isotopes found in nature have lower binding energies per nucleon than any other stable compound nuclides, save deuterium, and helium-3 (3He). Though very light in atomic weight, lithium is LESS COMMON in the solar system than 25 of the first 32 chemical elements. Because of its high reactivity, lithium only appears naturally in the form of compounds. Lithium occurs in a number of pegmatitic minerals, but is also commonly obtained from brines and clays.