The six elements of group 1A of the periodic table are called alkali metals. The five that are stable enough for study—lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs), in order of increasing chemical reactivity—are all highly reactive. They burn in air and react violently with water to form strong bases called alkalis in which the positive ion of the metal is combined with the negative hydroxide (OH) ion. The sixth alkali metal—francium (Fr)—is radioactive and so unstable that its longest-lived isotope has a half-life of only 22 minutes.
The alkali metals constitute Group 1A of the periodic table. In general, each alkali metal element is more reactive than its counterpart in the neighboring Group 2A.
Lithium
The lightest metal known, lithium is only half as heavy as the same volume of water. Like sodium, it reacts with water to release hydrogen, but without generating enough heat to ignite the gas. Lithium hydroxide draws carbon dioxide out of the air, so it serves as a filter in ventilating systems for spaceships and submarines. The metal is added to copper to create a strong, lightweight alloy. Lithium salts are used in batteries, enamels, glass, and ceramic products, and lithium carbonate is used in treating manic-depressive illness.
Sodium and potassium
Sodium is the sixth most abundant element, making up almost 3 per cent of the earth’s crust. In nature, it occurs mainly as sodium chloride—table salt—a major component of seawater. Sodium chloride is obtained by evaporation of seawater and by underground mining of halite, a mineral. Other natural sources of sodium include soda ash (a carbonate salt) and borax. Much of the sodium chloride produced is converted to sodium hydroxide (caustic soda) and chlorine, both of which have many industrial applications. Sodium compounds are used in making glass and ceramics, in household detergents, weedkillers, photographic chemicals, and in tanning leather. Some nuclear reactors use metallic sodium as a coolant. In animals, sodium as well as potassium are needed to maintain a normal flow of water between body fluids and cells and to help prevent excessive water loss. The two elements are also necessary for tissue formation, muscle contraction, and metabolism.
Rubidium, cesium, and francium
Although rubidium is widely distributed in the earth’s crust and even more abundant than lead, copper, or zinc, it is never found in concentrated form and is thus very costly to extract. Industrially, it is used in catalysts and photoelectric cells.
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