alkalimetal

An alkali metal is any element in Group 1 of the periodic table, excluding hydrogen. The naturally occurring alkali metals are lithium, sodium, potassium, rubidium, cesium, and francium. They are characterized by being soft metals with very low densities and low melting points compared with most other metals. All have a single valence electron and form the +1 oxidation state in compounds. Ionization energies decrease down the group, and reactivity with water increases down the group, making francium the most reactive under ordinary conditions. Because of their high reactivity with air and moisture, alkali metals are typically stored under oil or in an inert atmosphere.

In reactions, alkali metals readily lose their outer electron. With water they produce hydrogen gas and alkali metal hydroxide, releasing heat and sometimes igniting the hydrogen. They also react with oxygen to form oxides; heavier members can form peroxides or superoxides such as KO2, RbO2, and CsO2. In dioxygen atmospheres, surfaces quickly corrode, and the metals may ignite. They are not found free in nature but occur as salts in minerals. Industrial production involves electrolysis of molten salts or ores and recovery from brine streams.

Applications include lithium in rechargeable batteries and high-strength alloys; sodium or potassium compounds widely used in chemicals, glass production, and fertilizers; cesium and rubidium used in specialized research and atomic clocks; francium, detected only in trace amounts in minute quantities for research. The chemistry of alkali metals helps explain trends in reactivity and bonding among main-group elements.