|Name, Symbol, Number||rubidium, Rb, 37|
|Chemical series||alkali metals|
|Group, Period, Block||1, 5, s|
|Atomic mass||85.4678(3) g/mol|
|Electron configuration||[Kr] 5s1|
|Electrons per shell||2, 8, 18, 8, 1|
|Density (near r.t.)||1.532 g/cm³|
|Liquid density at m.p.||1.46 g/cm³|
|Melting point||312.46 K
(39.31 °C, 102.76 °F)
|Boiling point||961 K
(688 °C, 1270 °F)
2093 K, 16 MPa
|Heat of fusion||2.19 kJ/mol|
|Heat of vaporization||75.77 kJ/mol|
|Heat capacity||(25 °C) 31.060 J/(mol·K)|
|Crystal structure||cubic body centered|
(strongly basic oxide)
|Electronegativity||0.82 (Pauling scale)|
|1st: 403.0 kJ/mol|
|2nd: 2633 kJ/mol|
|3rd: 3860 kJ/mol|
|Atomic radius||235 pm|
|Atomic radius (calc.)||265 pm|
|Covalent radius||211 pm|
|Van der Waals radius||244 pm|
|Magnetic ordering||no data|
|Electrical resistivity||(20 °C) 128 nΩ·m|
|Thermal conductivity||(300 K) 58.2 W/(m·K)|
|Speed of sound (thin rod)||(20 °C) 1300 m/s|
|Speed of sound (thin rod)||(r.t.) 2.4 m/s|
|Bulk modulus||2.5 GPa|
|Brinell hardness||0.216 MPa|
|CAS registry number||7440-17-7|
Rubidium (chemical symbol Rb, atomic number 37) is a soft, silvery-white metallic element of the alkali metal group. Rb-87, a naturally occurring isotope, is (slightly) radioactive. Rubidium is very soft and highly reactive, with properties similar to other elements in group one, like rapid oxidation in air.
This element is considered to be the sixteenth most abundant element in the Earth's crust. It occurs naturally in the minerals leucite, pollucite, and zinnwaldite, which contains traces of up to one percent of its oxide. Lepidolite contains 1.5 percent rubidium and this is the commercial source of the element. Some potassium minerals and potassium chlorides also contain the element in commercially significant amounts. One notable source is also in the extensive deposits of pollucite at Bernic Lake, Manitoba.
Rubidium (L rubidus, deepest red) was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff in the mineral lepidolite through the use of a spectroscope. However, this element had minimal industrial use until the 1920s. Historically, the most important use for rubidium has been in research and development, primarily in chemical and electronic applications.
Rubidium is the second most electropositive of the stable alkaline elements and liquefies at high ambient temperature (102.7 F = 39.3 C). Like other group one elements this metal reacts violently in water. In common with potassium and cesium this reaction is usually vigorous enough to ignite the liberated hydrogen. Rubidium has also been reported to ignite spontaneously in air. Also like other alkali metals, it forms amalgams with mercury and it can form alloys with gold, caesium, sodium, and potassium. The element gives a reddish-violet color to a flame, hence its name.
When metallic rubidium reacts with oxygen, as in the tarnishing process, it produces the bronze-colored Rb6O and copper-colored Rb9O2. The final product is principally the superoxide, RbO2, which can then be reduced to Rb2O using excess rubidium metal.
There are 24 isotopes of rubidium known with naturally occurring rubidium being composed of just two isotopes; Rb-85 (72.2 percent) and the radioactive Rb-87 (27.8 percent). Normal mixes of rubidium are radioactive enough to fog photographic film in approximately 30 to 60 days.
Rb-87 has a half-life of 48.8×109 years. It readily substitutes for potassium in minerals, and is therefore fairly widespread. Rb has been used extensively in dating rocks; Rb-87 decays to stable strontium-87 by emission of a negative beta particle. During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Highest ratios (ten or higher) occur in pegmatites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the Sr-87/Sr-86 ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered. See Rubidium-Strontium dating for a more detailed discussion.
- Rubidium chloride (RbCl): In its gas phase, this salt exists as diatomic molecules, but as a solid it can take one of three arrangements (or polymorphs) as determined with holographic imaging. Solid RbCl is hygroscopic (absorbs moisture from the air), so it is usually protected from atmospheric moisture using a desiccator. It is primarily used in research laboratories. For instance, it is a good electrolyte for electrochemical experiments. For biological and biomedical research, it is used to test the genetic transformation of cells and as a noninvasive biomarker. Infusing tumor cells with rubidium chloride increases their pH.
- Rubidium hydroxide (RbOH): It is a strong alkali that is formed by dissolving rubidium oxide in water. It is a highly reactive and corrosive compound that burns the skin immediately on contact. It must therefore be handled with extreme care, using protective clothing, gloves, and eye-face protection. It is used mainly in scientific research. Synthesis of nearly all rubidium compounds involves rubidium hydroxide as an intermediate. Rubidium oxide is added to water, and the two react to produce the soluble hydroxide.
- Rubidium oxide (Rb2O): This yellow colored solid (STP) is the simplest oxide of rubidium. Like other alkali metal oxides, it is a strong base. It thus reacts rapidly with water to form rubidium hydroxide (RbOH), releasing heat. Rubidium oxide is potentially dangerous because, like other strongly alkaline compounds, skin contact can cause burns.
Potential or current uses of rubidium include:
- A working fluid in vapor turbines.
- A getter in vacuum tubes.
- A photocell component.
- The resonant element in atomic clocks. This is due to the hyperfine structure of Rubidium's energy levels.
- An ingredient in special types of glass.
- The production of superoxide by burning in oxygen.
- The study of potassium ion channels in biology.
Rubidium compounds are sometimes used in fireworks to give them a purple color.
Rubidium has also been considered 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, particularly 87Rb, in the form of vapor, is one of the most commonly-used atomic species employed for laser cooling and Bose-Einstein condensation. Its desirable features for this application include the ready availability of inexpensive diode laser light at the relevant wavelength, and the moderate temperatures required to obtain substantial vapor pressures.
Rubidium has been used for polarizing 3He (that is, producing volumes of magnetized 3He gas, with the nuclear spins aligned toward a particular direction in space, rather than randomly). Rubidium vapor is optically pumped by a laser and the polarized Rb polarizes 3He by the hyperfine interaction. Spin-polarized 3He cells are becoming popular for neutron polarization measurements and for producing polarized neutron beams for other purposes.
Rubidium, like sodium and potassium, is almost always in its +1 oxidation state. The human body tends to treat Rb+ ions as if they were potassium ions, and therefore concentrates rubidium in the body's electrolytic fluid. The ions are not particularly toxic, and are relatively quickly removed in the sweat and urine. However, taken in excess it can be dangerous.
- ^ Lide, D.R., P. Cahill, and JL.P. Gold. 1963. Cohesion and polymorphism in solid rubidium chloride Journal of Chemical Physics 40, pp. 156-159. Retrieved January 6, 2008.
- ^ Kopecky, M., J. Fábry, J. Kub, E. Busetto, and A. Lausi. 2005. X-ray diffuse scattering holography of a centrosymmetric sample Applied Physics Letters, 87 3p. Retrieved January 6, 2008.
- ^ Hougardy, E., P. Pernet, M. Warnau, J. Delisle, and J.C. Grégoire. 2003. Marking bark beetle parasitoids within the host plant with rubidium for dispersal studies Entomologia Experimentalis et Applicata 108, pp. 107. Retrieved January 6, 2008.
- Greenwood, N.N. and A. Earnshaw. 1998. Chemistry of the Elements, 2nd Edition. Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654
- Holleman, A. F. and E. Wiberg. "Inorganic Chemistry". Academic Press: San Diego, 2001.
- Meites, Louis. Handbook of Analytical Chemistry. New York: McGraw-Hill Book Company, 1963.
- Nechamkin H. The Chemistry of the Elements. New York: McGraw-Hill, 1968.
- Rubidium Los Alamos National Laboratory. Retrieved January 6, 2008.
- Rubidium oxide at Engineering Database Retrieved January 6, 2008.
- Rubidium oxide at WebElements Retrieved January 6, 2008.
- Rubidium oxide at Fisher Scientific Retrieved January 6, 2008.
- Rubidium hydroxide at ChemExper Retrieved January 6, 2008.
- WebElements.com – Rubidium Retrieved January 6, 2008.
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