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Rubidium is a chemical element with symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group, with an atomic mass of 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, such as very rapid oxidation in air. Natural rubidium is a mix of two isotopes: 85Rb, the only stable one, constitutes 72% of it. The remaining 28% is the slightly radioactive 87Rb with a half-life of 49 billion years—more than three times longer than the estimated age of the universe. German chemists Robert Bunsen and Gustav Kirchhoff discovered rubidium in 1861 by the newly developed method of flame spectroscopy. Rubidium's compounds have various chemical and electronic applications. Rubidium metal is easily vaporized and has a convenient spectral absorption range, making it a frequent target for laser manipulation of atoms. Rubidium is not known to be necessary for any living organisms. However, rubidium ions are handled by living organisms in a manner similar to potassium ions, being actively taken up by plants and by animal cells due to their identical charge. ==Characteristics== Rubidium is a very soft, ductile, silvery-white metal.〔 It is the second most electropositive of the non-radioactive alkali metals and melts at a temperature of . Similar to other alkali metals, rubidium metal reacts violently with water, forms amalgams with mercury and alloys with gold, iron, caesium, sodium, and potassium, but not lithium (even though rubidium and lithium are in the same group). As with potassium (which is slightly less reactive) and caesium (which is slightly more reactive), rubidium's reaction with water is usually vigorous enough to ignite the hydrogen gas it liberates. Rubidium has also been reported to ignite spontaneously in air. Rubidium has a very low ionization energy of only 406 kJ/mol. Rubidium and potassium show a very similar purple color in the flame test, which makes spectroscopy methods necessary to distinguish the two elements. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「rubidium」の詳細全文を読む スポンサード リンク
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