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Atomic Number: 37
Atomic Symbol: Rb
Atomic Weight: 85.4678
Electron Configuration: [Kr]5s1
History
(L. rubidus, deepest red) Discovered in 1861 by Bunsen and Kirchoff
in the mineral lepidolite by use of the spectroscope.
Sources
The element is much more abundant than was thought several years ago.
It is now considered to be the 16th most abundant element in the earth's crust.
Rubidium occurs in pollucite, leucite, and zinnwaldite, which contains traces up
to 1%, in the form of the oxide. It is found in lepidolite to the extent of
about 1.5%, and is recovered commercially from this source. Potassium minerals,
such as those found at Searles Lake, California, and potassium chloride
recovered from the brines in Michigan also contain the element and are
commercial sources. It is also found along with cesium in the extensive deposits
of pollucite at Bernic Lake, Manitoba.
Properties
Rubidium can be liquid at room temperature. It is a soft,
silvery-white metallic element of the alkali group and is the second most
electropositive and alkaline element. It ignites spontaneously in air and reacts
violently in water, setting fire to the liberated hydrogen. As with other alkali
metals, it forms amalgams with mercury and it alloys with gold, cesium, sodium,
and potassium. It colors a flame yellowish violet. Rubidium metal can be
prepared by reducing rubidium chloride with calcium, and by a number of other
methods. It must be kept under a dry mineral oil or in a vacuum or inert
atmosphere.
Isotopes
Twenty four isotopes of rubidium are known. Naturally occurring
rubidium is made of two isotopes, 85Rb and 87Rb.
Rubidium-87 is present to the extent of 27.85% in natural rubidium and is a beta
emitter with a half-life of 4.9 x 1010 years. Ordinary rubidium is sufficiently
radioactive to expose a photographic film in about 30 to 60 days. Rubidium forms
four oxides: Rb2O, Rb2O2, Rb2O3,
Rb2O4.
Uses
Because rubidium can be easily ionized, it has been considered for
use in "ion engines" for space vehicles; however, cesium is somewhat more
efficient for this purpose. It is also proposed for use as a working fluid for
vapor turbines and for use in a thermoelectric generator using the
magnetohydrodynamic principle where rubidium ions are formed by heat at high
temperature and passed through a magnetic field. These conduct electricity and
act like an armature of a generator thereby generating an electric current.
Rubidium is used as a getter in vacuum tubes and as a photocell component. It
has been used in making special glasses. RbAg4I5 is
important, as it has the highest room conductivity of any known ionic crystal.
At 20° C its conductivity is about the same as
dilute sulfuric acid. This suggests use in thin film batteries and other
applications.
Sources: CRC Handbook of Chemistry and
Physics and the American Chemical Society.
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