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Rubidium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                37             krypton ← rubidium → strontium
                 K
                ↑
                Rb
                ↓
                Cs

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                     Name, Symbol, Number rubidium, Rb, 37
                                             Chemical series alkali metals
                                              Group, Period, Block 1, 5, s
                                                     Appearance grey white
                                             Atomic mass 85.4678 (3) g/mol
                                          Electron configuration [Kr] 5s^1
                                        Electrons per shell 2, 8, 18, 8, 1
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 1.532 g·cm^−3
                                    Liquid density at m.p. 1.46 g·cm^−3
                                                   Melting point 312.46  K
                                                 (39.31 ° C, 102.76 ° F)
                                                       Boiling point 961 K
                                                     (688 ° C, 1270 ° F)
                                             Critical point (extrapolated)
                                                            2093 K, 16 MPa
                                          Heat of fusion 2.19 kJ·mol^−1
                                   Heat of vaporization 75.77 kJ·mol^−1
                         Heat capacity (25 °C) 31.060 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                          P/Pa   1  10  100 1 k 10 k 100 k
                                         at T/K 434 486 552 641 769   958

                                                         Atomic properties
                                     Crystal structure cubic body centered
                                                        Oxidation states 1
                                                    (strongly basic oxide)
                                    Electronegativity 0.82 (Pauling scale)
                                                       Ionization energies
                                           ( more) 1st: 403.0 kJ·mol^−1
                                                    2nd: 2633 kJ·mol^−1
                                                    3rd: 3860 kJ·mol^−1
                                                      Atomic radius 235 pm
                                              Atomic radius (calc.) 265 pm
                                                    Covalent radius 211 pm
                                               Van der Waals radius 244 pm
                                                             Miscellaneous
                                                 Magnetic ordering no data
                                Electrical resistivity (20 °C) 128 nΩ·m
                       Thermal conductivity (300 K) 58.2 W·m^−1·K^−1
                               Speed of sound (thin rod) (20 °C) 1300 m/s
                                                   Young's modulus 2.4 GPa
                                                      Bulk modulus 2.5 GPa
                                                         Mohs hardness 0.3
                                                Brinell hardness 0.216 MPa
                                             CAS registry number 7440-17-7
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of rubidium

                           iso    NA     half-life   DM   DE ( MeV)   DP
                          ^83Rb syn     86.2 d       ε   -           ^83Kr
                                                     γ   0.52, 0.53,
                                                         0.55        -
                          ^84Rb syn     32.9 d       ε   -           ^84Kr
                                                     β^+ 1.66, 0.78  ^84Kr
                                                     γ   0.881       -
                                                     β^- 0.892       ^84Sr
                          ^85Rb 72.168% Rb is stable with 48 neutrons
                          ^86Rb syn     18.65 d      β^- 1.775       ^86Sr
                                                     γ   1.0767      -
                          ^87Rb 27.835% 4.88×10^10 y β^- 0.283       ^87Sr

                                                                References

   Rubidium ( IPA: /ruːˈbɪdiəm, rəˈbɪdiəm/) is a chemical element in the
   periodic table that has the symbol Rb and atomic number 37. Rb 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 1, like rapid oxidation in air.

Notable characteristics

   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 1 elements this metal reacts violently in water. In
   common with potassium and caesium 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
   colour to a flame, hence its name.

Uses

   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 is easily ionized, so it has been considered for use in ion
   engines for space vehicles (but caesium and xenon are more efficient
   for this purpose).

   Rubidium compounds are sometimes used in fireworks to give them a
   purple colour.

   RbAg[4]I[5] has the highest room temperature conductivity of any known
   ionic crystal. This property could be useful in thin film batteries and
   in other applications.

   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 .

History

   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.

Occurrence

   This element is considered to be the 16th most abundant element in the
   earth's crust. It occurs naturally in the minerals leucite, pollucite,
   and zinnwaldite, which contains traces of up to 1% of its oxide.
   Lepidolite contains 1.5% 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 metal can be produced by reducing rubidium chloride
   with calcium among other methods. Rubidium forms at least four oxides:
   Rb[2]O, Rb[2]O[2], Rb[2]O[3], RbO[2]. In 1997 the cost of this metal in
   small quantities was about US$ 25/ gram.

Isotopes

   There are 24 isotopes of rubidium known with naturally occurring
   rubidium being composed of just two isotopes; Rb-85 (72.2%) and the
   radioactive Rb-87 (27.8%). Normal mixes of rubidium are radioactive
   enough to fog photographic film in approximately 30 to 60 days.

   Rb-87 has a half-life of 48.8×10^9 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 (10 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's most common compounds are RbCl, RbF, and Rb[2]SO[4].

Precautions

   Rubidium reacts violently with water and can cause fires. To ensure
   both safety and purity, this element must be kept under a dry mineral
   oil, in a vacuum or in an inert atmosphere.

Biological Effects

   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.

   Retrieved from " http://en.wikipedia.org/wiki/Rubidium"
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