The alkali metals are a group of elements that are classified together in the periodic table, where they form group 1A. In order of increasing weight of their atoms, the alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). Sodium and potassium are the most important members of the group. All are extremely light, silver-white metals—lithium, with a density half that of water, is the lightest solid element. Cesium, the heaviest of the group, has a relative density of 1.87.
Alkali metals are all soft enough to be cut easily with a knife. They conduct heat and electricity well and are easy to melt and vaporize at comparatively low temperatures, forming gases with molecules consisting of two atoms.
These metals are never found in a pure form in nature, since they are extremely reactive and even react violently with water, forming hydroxides and releasing hydrogen. For this reason and because of their softness, they are useless as structural metals in spite of their lightness. Cesium bursts into flames even in moist air. Alkali metals therefore must be isolated from moisture, so they are stored under paraffin or in sealed evacuated containers.
Their reactivity is due to the fact that the lone outer electron of each of their atoms is unusually easy to detach, transforming the atom into an ion with a single positive charge and thus giving it a strong tendency to combine with the negative ions of other elements. These ionic bonds are very strong, making it difficult to split these compounds to obtain pure alkali elements. Alkali metals cannot be isolated by normal electrolysis since this process involves the use of water, with which the extracted pure metal would immediately react. Instead, it is done by the electrolysis of the compound after it has been melted to make it liquid.
The tendency of the metals to give off electrons makes them useful in photoelectric cells and television camera tubes, usually in the form of a thin film deposited on glass.
Lithium
Lithium, the lightest element of the group, is in some ways more like the elements of the next group in the periodic table, the alkaline earth metals. In particular, its carbonate and phosphate are only sparingly soluble in water. Lithium carbonate is the most widely used lithium compound. It is incorporated in glass ceramics such as cooking ware and modern flat-top stoves because it imparts resistance to thermal cracking and is used as a flux to lower operating temperatures in aluminum reduction cells.
Lithium soaps, such as lithium stearate, are used as gelling agents to solidify greases. Lithium hydride is used as a source of hydrogen, such as that used in meteorological balloons:
Lithium salts are used in fireworks to give red colors. In medicine, the salts have been used for the treatment of rheumatism.
Important future uses are in the manufacture of lightweight, rechargeable batteries, which may be used in electric vehicles, and in the longer term, lithium has a potential role in thermonuclear fusion, a vast future energy source. The fusion system—a reaction between deuterium and tritium (heavy isotopes of hydrogen)—appears feasible, and tritium is obtainable from lithium.
Lithium is found in naturally occurring complex silicate minerals such as spodumene, Li2OAl2O34SiO2—written LiAl(SiO3)2—and in brines. Lithium is recovered from spodumene by first roasting the mineral and then bleaching it with acid. The sparingly soluble carbonate can be precipitated (solidified) and dissolved in acids to form other salts. Metallic lithium is obtained by electrolysis of the chloride, LiCl, fused with potassium chloride, KCl, to lower the melting point. The molten lithium rises to the surface and is collected under a bell to prevent it with acid. The sparingly soluble carbonate can be precipitated (solidified) and dissolved in acids to form other salts. Metallic lithium is obtained by electrolysis of the chloride, LiCl, fused with potassium chloride, KCl, to lower the melting point. The molten lithium rises to the surface and is collected under a bell to prevent it from coming into contact with the air.
