Considered the lightest solid element on earth. Li. Discovered 1817. One reasonably could assume that after decades of brilliant achievement, lithium had lived its finest hour. But the assumption is without merit. Lithium's boundaries today are wider than yesterday. Lithium's potential today is greater than yesterday. Lithium's caretakers today see a more distant horizon than yesterday.
Lithium is a metal. The lightest of all solid elements, it floats on gasoline. It is quite soft, yet when combined with magnesium, the resulting alloy is so tough it has been used experimentally as armor plate. Lithium metal is also highly reactive. Reactions of lithium metal with water, oxygen, carbon dioxide and a host of other elements - even nitrogen - are possible at room temperatures. Yet many lithium compounds, especially those formulated for the ceramics industries, are as inert as common sand. This seemingly paradoxical behavior makes lithium extremely useful. Part of the paradox can be explained by examining basic lithium chemistry.
Lithium (atomic number 3, atomic weight 6.941) is a silvery-white metal, slightly harder than sodium but softer than lead. It is extremely light; its density being 0.531 g/cm¸ or about half that of water. Lithium appears in the periodic table as the first element in Group I, the alkali metals group. Like the other metals in the group - sodium, potassium, rubidium and cesium - it is so chemically active that, in nature, it never occurs as a pure element, but is always bound in stable minerals or salts.
In some of its compounds, however, lithium shows a great resemblance to Group II, or alkaline earth metals. For example, the water solubility of lithium hydroxide is substantially lower than that of other alkali hydroxides. In general, lithium's physical and chemical properties stem from its atomic structure. A single atom of lithium consists of a nucleus (three protons and either three or four neutrons) with three electrons orbiting in two shells. The inner shell (the helium shell) contains two electrons and is chemically inert. The outer shell contains only one electron.
Lithium, more than any other alkali metal, tends to eject this electron from its outermost shell. The resulting lithium-ion carries a positive charge (+1). In solid metal, individual lithium atoms are arranged geometrically in a cubic lattice and can transfer a negative charge from place to place. This electron movement makes lithium metal an excellent electrical conductor.