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Alkali Metals - Lithium, Sodium, Potassium, Rubidium And Cesium - Francium

Science EncyclopediaScience & Philosophy: Adrenoceptor (adrenoreceptor; adrenergic receptor) to Ambient

The first column on the periodic table of the chemical elements is collectively called the alkali metal group: lithium, sodium, potassium, rubidium, cesium, and francium. Because their outer electron structure is similar, they all have somewhat similar chemical and physical properties. All are shiny, soft enough to cut with a knife, and most are white (cesium is yellow-white). All react with water to give hydrogen gas and the metal hydroxide; the heavier alkali metals react with such vigorous evolution of heat that the hydrogen often bursts into flame. They also react with the oxygen in the air to give either an oxide, peroxide, or superoxide, depending on the metal. Alkali metals almost always form ions with a positive (+1) charge, and are so reactive as elements that virtually all occur in nature only in compound form. Sodium is the most abundant, followed by potassium, rubidium, lithium, and cesium. Francium is intensely radioactive and extremely rare; only the tiniest traces occur in the earth's crust.

Most of the alkali metals glow with a characteristic color when placed in a flame; lithium is bright red, sodium gives off an intense yellow, potassium is violet, rubidium is a dark red, and cesium gives off blue light. These flame tests are useful for identifying the metals. Additionally, a striking use of sodium's characteristic emitted yellow light is in highly specialized lightbulbs, such as the very bright sodium vapor lights that appear along highways. In these bulbs, sodium atoms are excited with electricity, not a flame. Lightbulbs made with sodium use less electricity than conventional bulbs and are brighter, because the sodium gives off a larger percentage of its energy as light rather than heat.


Francium

Marguerite Perey discovered francium (Fr) in 1939, and named it after her homeland, France. Almost no francium occurs naturally on the earth, except very small amounts in uranium ores. Additionally, it is very radioactive, so the very tiny amounts produced by bombarding radium with neutrons are used almost exclusively for pure research. Presumably its chemistry resembles the other alkali metals, although much of that remains speculative.

Resources

Books

Emsley, John. The Elements. 3rd ed. New York: Oxford University Press, Inc., 1998.

Greenwood, N. N. and A. Earnshaw. Chemistry of the Elements. New York: Butterworth-Heinemann, 1997.


Gail B. C. Marsella

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