Rubidium
Introduction
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a very soft, silvery-white metal in the alkali metal group. It is one of the most electropositive and alkaline elements. It ignites spontaneously in air and reacts violently with water, setting fire to the liberated hydrogen. As with other alkali metals, it forms amalgams with mercury and it alloys with gold, caesium, sodium, and potassium.
History
Rubidium was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff, in the mineral lepidolite through the use of a spectroscope. The name comes from the Latin word 'rubidus', meaning dark red or deepest red, referencing the deep red lines in its emission spectrum.
Occurrence and production
Rubidium is the twenty-third most abundant element in the Earth's crust, approximately as common as zinc and rather more common than copper. It occurs naturally in the minerals leucite, pollucite, and zinnwaldite, which contain up to 1% rubidium, and in lepidolite to a lesser extent (up to 0.03% rubidium). This metal is produced by electrolysis of its hydroxide and is often obtained as a byproduct of lithium production.
Properties and reactions
Rubidium is a very soft, ductile, silvery-white metal. It is the second most electropositive of the stable alkali metals and melts at a temperature of 39.3 °C (102.7 °F). Like other alkali metals, rubidium metal reacts violently with water. As with potassium (which is slightly less reactive) and caesium (which is slightly more reactive), this reaction is usually vigorous enough to ignite the hydrogen gas it produces. Rubidium has also been reported to ignite spontaneously in air.
Compounds
Rubidium forms a large number of compounds, although none of them has any significant commercial use. Some of the common compounds are rubidium chloride (RbCl), rubidium monoxide (Rb2O), and rubidium copper sulfate Rb2SO4·CuSO4·6H2O. Rubidium compounds are sometimes used in fireworks to give them a purple color.
Applications
Rubidium has been used in creating electron tubes and photoelectric cells. In particular, rubidium-87 has a half-life of 48.8 billion years, which is more than three times the estimated age of the universe. This has made rubidium useful in dating geological and archaeological specimens. Rubidium compounds are used in glasses and ceramics and in fireworks to give a purple color. Rubidium is also used as a getter in vacuum tubes and as a photocell component.
Biological role and precautions
Rubidium is not known to be necessary for any living organisms. However, rubidium ions have the same charge as potassium ions and are actively taken up and treated by animal cells in similar ways. Rubidium is not a known environmental hazard or health hazard. It is slightly radioactive but would have to be ingested in large amounts to cause a radiation hazard.