   #copyright

Caesium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                55                xenon ← caesium → barium
                Rb
                ↑
                Cs
                ↓
                Fr

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                      Name, Symbol, Number caesium, Cs, 55
                                             Chemical series alkali metals
                                              Group, Period, Block 1, 6, s
                                                   Appearance silvery gold
                                         Atomic mass 132.9054519 (2) g/mol
                                          Electron configuration [Xe] 6s^1
                                    Electrons per shell 2, 8, 18, 18, 8, 1
                                                       Physical properties
                                                               Phase solid
                                       Density (near r.t.) 1.93 g·cm^−3
                                   Liquid density at m.p. 1.843 g·cm^−3
                                                   Melting point 301.59  K
                                                  (28.44 ° C, 83.19 ° F)
                                                       Boiling point 944 K
                                                     (671 ° C, 1240 ° F)
                                            Critical point 1938 K, 9.4 MPa
                                          Heat of fusion 2.09 kJ·mol^−1
                                    Heat of vaporization 63.9 kJ·mol^−1
                         Heat capacity (25 °C) 32.210 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                          P/Pa   1  10  100 1 k 10 k 100 k
                                         at T/K 418 469 534 623 750   940

                                                         Atomic properties
                                     Crystal structure body centered cubic
                                                        Oxidation states 1
                                                    (strongly basic oxide)
                                    Electronegativity 0.79 (Pauling scale)
                                     Ionization energies 1st: 375.7 kJ/mol
                                                        2nd: 2234.3 kJ/mol
                                                          3rd: 3400 kJ/mol
                                                      Atomic radius 260 pm
                                              Atomic radius (calc.) 298 pm
                                                    Covalent radius 225 pm
                                                             Miscellaneous
                                                 Magnetic ordering no data
                                Electrical resistivity (20 °C) 205 nΩ·m
                       Thermal conductivity (300 K) 35.9 W·m^−1·K^−1
                         Thermal expansion (25 °C) 97 µm·m^−1·K^−1
                                                   Young's modulus 1.7 GPa
                                                      Bulk modulus 1.6 GPa
                                                         Mohs hardness 0.2
                                                 Brinell hardness 0.14 MPa
                                             CAS registry number 7440-46-2
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of caesium

                             iso    NA    half-life   DM  DE ( MeV)   DP
                            ^133Cs 100%  Cs is stable with 78 neutrons
                            ^134Cs syn   65.159 Ms
                                         (2.0648 y)   ε   1.229     ^134Xe
                                                      β^- 2.059     ^134Ba
                            ^135Cs trace 73 Ts
                                         (2,300,000y) β^- 0.269     ^135Ba
                            ^137Cs syn   948.9 Ms
                                         (30.07y)     β^- 1.176     ^137Ba

                                                                References

   Caesium (also spelled cesium, IPA: /ˈsiːziəm/) is a chemical element in
   the periodic table that has the symbol Cs and atomic number 55. It is a
   soft silvery-gold alkali metal with a melting point of 28 °C (83 °F)
   which makes it one of the metals that are liquid at or near room
   temperature along with rubidium (39°C), francium (27 °C), mercury (-39
   °C), and gallium (30 °C). This element is most notably used in atomic
   clocks.

   The variant spelling cesium is sometimes used, especially in North
   American English, but caesium is the spelling used by the IUPAC,
   although since 1993 it has recognized cesium as a variant as well.

Notable characteristics

   The electromagnetic spectrum of caesium has two bright lines in the
   blue part of the spectrum along with several other lines in the red,
   yellow, and green. This metal is silvery gold in colour and is both
   soft and ductile. Caesium is also the most electropositive and most
   alkaline of the stable chemical elements and has the second lowest
   ionization potential (francium being the lowest). Caesium is the least
   abundant of the five non-radioactive alkali metals. (Technically,
   francium is the least common alkali metal, but since it is highly
   radioactive with an estimated 340 to 550 grams in the entire earth at
   one time, its abundance can be considered zero in practical terms.)

   Along with gallium, francium, and mercury, caesium is among the only
   metals that are liquid at or near room temperature. Caesium reacts
   explosively in cold water and also reacts with ice at temperatures
   above −116°C.

   Caesium hydroxide (CsOH) is a very strong base and will rapidly etch
   the surface of glass. CsOH is often stated to be the "strongest base"
   (after FrOH), but in fact many compounds such as n-butyllithium and
   sodium amide are stronger.

   There is an account that caesium, reacting with fluorine, takes up more
   fluorine than it stoichometrically should. It is possible that, after
   the salt Cs^+F^− has formed, the Cs^+ ion, which has the same
   electronic structure as elemental xenon, can like xenon be oxidised
   further by fluorine and form traces of a higher fluoride such as
   CsF[3], analogous to XeF[2].

Applications

   Probably the most widespread use of caesium today is in caesium
   formate-based drilling fluids for the oil industry. The high density of
   the caesium formate brine (up to 2.3 sg,) coupled with the relative
   benignity of ^133Cs , reduces the requirement for toxic high-density
   suspended solids in the drilling fluid, which is a significant
   technological, engineering and environmental advantage.

   Caesium is also notably used in atomic clocks, which are accurate to
   seconds in many thousands of years. Since 1967, the International
   System of Measurements bases its unit of time, the second, on the
   properties of caesium. SI defines the second as 9,192,631,770 cycles of
   the radiation which corresponds to the transition between two electron
   spin energy levels of the ground state of the ^133Cs atom.
     * ^134Cs has been used in hydrology as a measure of caesium output by
       the nuclear power industry. This isotope is used because, while it
       is less prevalent than either ^133Cs or ^137Cs, ^134Cs can be
       produced solely by nuclear reactions. ^135Cs has also been used in
       this function.
     * Like other group 1 elements, caesium has a great affinity for
       oxygen and is used as a " getter" in vacuum tubes.
     * This metal is also used in photoelectric cells due to its ready
       emission of electrons.
     * Caesium is used as a catalyst in the hydrogenation of certain
       organic compounds.
     * Radioactive isotopes of caesium are used in the medical field to
       treat certain types of cancer.
     * Caesium fluoride is widely used in organic chemistry as a base and
       as a source of anhydrous fluoride ion.
     * Caesium vapor is used in many common magnetometers.
     * Because of their high density, caesium chloride solutions are
       commonly used in molecular biology for density gradient
       ultracentrifugation, primarily for the isolation of viral
       particles, subcellular organelles and fractions, and nucleic acids
       from biological samples.
     * Cesium nitrate is used as oxidiser to burn silicon in infrared
       flares like the LUU-19 flare, because it emits much of its light in
       the near infrared spectrum.
     * More recently this metal has been used in ion propulsion systems.
     * Caesium-137 is an extremely common radioisotope used as a
       gamma-emitter in industrial applications such as:
          + moisture density gauges
          + leveling gauges
          + thickness gauges
          + well-logging devices (used to measure the thickness of
            rock-strata)
     * also used as an internal standard in spectrophotometry

History

   Caesium (Latin caesius meaning "sky blue" or "light blue") was
   spectroscopically discovered by Robert Bunsen and Gustav Kirchhoff in
   1860 in mineral water from Dürkheim, Germany. Its identification was
   based upon the bright blue lines in its spectrum and it was the first
   element discovered by spectrum analysis. The first caesium metal was
   produced in 1882 by Carl Setterberg. Historically, the most important
   use for caesium has been in research and development, primarily in
   chemical and electrical applications.

Occurrence

   Pollucite, a caesium mineral
   Enlarge
   Pollucite, a caesium mineral

   An alkali metal, caesium occurs in lepidolite, pollucite ( hydrated
   silicate of aluminium and caesium) and within other sources. One of the
   world's most significant and rich sources of this metal is located at
   Bernic Lake in Manitoba. The deposits there are estimated to contain
   300,000 metric tons of pollucite at an average of 20% caesium.

   It can be isolated by electrolysis of fused caesium cyanide and in a
   number of other ways. Exceptionally pure and gas-free caesium can be
   made by the thermal decomposition of caesium azide. The primary
   compounds of caesium are caesium chloride and its nitrate. The price of
   caesium metal in 1997 was about $US 30 per gram, but its compounds are
   much cheaper.

   See also Caesium minerals.

Isotopes

   Caesium has at least 39 known isotopes, which is more than any other
   element except francium. The atomic masses of these isotopes range from
   112 to 151. Even though this element has a large number of isotopes, it
   has only one naturally occurring stable isotope, ^133Cs. Most of the
   other isotopes have half-lives from a few days to fractions of a
   second. The radiogenic isotope ^137Cs has been used in hydrologic
   studies, analogous to the use of ^3H. ^137Cs is produced from the
   detonation of nuclear weapons and is produced in nuclear power plants,
   and notably from the 1986 Chernobyl meltdown. Beginning in 1945 with
   the commencement of nuclear testing, ^137Cs was released into the
   atmosphere where it is absorbed readily into solution and is returned
   to the surface of the earth as a component of radioactive fallout. Once
   ^137Cs enters the ground water, it is deposited on soil surfaces and
   removed from the landscape primarily by particle transport. As a
   result, the input function of these isotopes can be estimated as a
   function of time. Caesium-137 has a half-life of 30.17 years. It
   decomposes to barium-137m (a short-lived product of decay) then to a
   form of nonradioactive barium.

Precautions

   All alkaline metals are highly reactive. Caesium, being one of the
   heavier alkaline metals, is also one of the most reactive and is highly
   explosive when it comes in contact with water (even cold water, or
   ice). Caesium hydroxide is an extremely strong base, and can attack
   glass.

   Caesium compounds are encountered rarely by most people. All caesium
   compounds should be regarded as mildly toxic because of its chemical
   similarity to potassium. Large amounts cause hyperirritability and
   spasms, but such amounts would not ordinarily be encountered in natural
   sources, so Cs is not a major chemical environmental pollutant. Rats
   fed caesium in place of potassium in their diet die, so this element
   cannot replace potassium in function.

   The isotopes ^134Cs and ^137Cs (present in the biosphere in small
   amounts as a result of radiation leaks) represent a radioactivity
   burden which varies depending on location. Radiocaesium does not
   accumulate in the body as effectively as many other fission products
   (such as radioiodine and radiostrontium), which are actively
   accumulated by the body.

   Retrieved from " http://en.wikipedia.org/wiki/Caesium"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
   of authors and sources) and is available under the GNU Free
   Documentation License. See also our Disclaimer.
