Rubidium

Rubidium

Rubidium is a chemical element with the 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 elements in Group 1, such as very rapid oxidation in air. Rubidium has only one stable isotope, 85Rb, with the isotope 87Rb, which composes almost 28% of naturally occurring rubidium, being slightly radioactive 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, like caesium, rubidium ions are handled by living organisms in a manner similar to potassium ions, being actively taken up by plants and by animal cells.

Occurrence


Rubidium is the twenty-third most abundant element in the Earth's crust, roughly as abundant as zinc and rather more common than copper. It occurs naturally in the minerals leucite, pollucite, carnallite, and zinnwaldite, which contain up to 1% of its oxide. Lepidolite contains between 0.3% and 3.5% rubidium, and is the commercial source of the element. Some potassium minerals and potassium chlorides also contain the element in commercially significant amounts.

Seawater contains an average of 125 µg/L of rubidium compared to the much higher value for potassium of 408 mg/L and the much lower value of 0.3 µg/L for caesium

Because of its large ionic radius, rubidium is one of the "incompatible elements." During magma crystallization, rubidium is concentrated together with its heavier analogue caesium in the liquid phase and crystallizes last. Therefore the largest deposits of rubidium and caesium are zone pegmatite ore bodies formed by this enrichment process. Because rubidium substitutes for potassium in the crystallization of magma, the enrichment is far less effective than in the case of caesium. Zone pegmatite ore bodies containing mineable quantities of caesium as pollucite or the lithium minerals lepidolite are also a source for rubidium as a by-product.

Two notable sources of rubidium are the rich deposits of pollucite at Bernic Lake, Manitoba, Canada, and the rubicline ((Rb,K)AlSi3O8) found as impurities in pollucite on the Italian island of Elba, with a rubidium content of 17.5%. Both of these deposits are also sources of caesium.

Symbol		Rb
Atomic Number		37
Atomic Weight		85.4678
Oxidation States		+1
Electronegativity, Pauling		0.82
State at RT		Solid, Metal
Melting Point, K		312.2
Boiling Point, K		961

Appearance and Characteristics

Harmful effects:

Rubidium is not known to be toxic.

Characteristics:

• Rubidium is a soft, silvery-white metallic element. It is solid at room temperature but melts easily, at 39.3 oC.
• Like the other group 1 metals, rubidium reacts violently with water, forming corrosive rubidium hydroxide (RbOH) and hydrogen gas, which is ignited by the heat of the reaction.
• Rubidium can also ignite spontaneously in air. It forms alloys with cesium, gold, sodium, and potassium and it forms amalgams with mercury.
• Rubidium burns with a reddish-violet flame color.

Uses of Rubidium

• Rubidium is used in photocells, as a getter (remover of trace gases) in vacuum tubes and as working fluid in vapor turbines.
• Rubidium-87 is slightly radioactive and has been used extensively in dating rocks.
• Rubidium compounds give a purple color in fireworks.
• Rubidium salts are used in glasses and ceramics.