   #copyright

Xenon

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                54                iodine ← xenon → caesium
                Kr
                ↑
                Xe
                ↓
                Rn

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                        Name, Symbol, Number xenon, Xe, 54
                                               Chemical series noble gases
                                             Group, Period, Block 18, 5, p
                                                      Appearance colorless
                                             Atomic mass 131.293 (6) g/mol
                               Electron configuration [Kr] 4d^10 5s^2 5p^6
                                       Electrons per shell 2, 8, 18, 18, 8
                                                       Physical properties
                                                                 Phase gas
                                              Density (0 °C, 101.325 kPa)
                                                                 5.894 g/L
                                                    Melting point 161.4  K
                                                (-111.7 ° C, -169.1 ° F)
                                                    Boiling point 165.03 K
                                              (-108.12 ° C, -162.62 ° F)
                                        Critical point 289.77 K, 5.841 MPa
                                          Heat of fusion 2.27 kJ·mol^−1
                                   Heat of vaporization 12.64 kJ·mol^−1
                         Heat capacity (25 °C) 20.786 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                            P/Pa  1  10 100 1 k 10 k 100 k
                                           at T/K 83 92 103 117 137   165

                                                         Atomic properties
                                     Crystal structure cubic face centered
                                    Oxidation states 0, +1, +2, +4, +6, +8
                                                      (rarely more than 0)
                                                     (weakly acidic oxide)
                                     Electronegativity 2.6 (Pauling scale)
                                    Ionization energies 1st: 1170.4 kJ/mol
                                                        2nd: 2046.4 kJ/mol
                                                        3rd: 3099.4 kJ/mol
                                              Atomic radius (calc.) 108 pm
                                                    Covalent radius 130 pm
                                               Van der Waals radius 216 pm
                                                             Miscellaneous
                                             Magnetic ordering nonmagnetic
                      Thermal conductivity (300 K) 5.65 mW·m^−1·K^−1
                                          Speed of sound (liquid) 1090 m/s
                                             CAS registry number 7440-63-3
                                                         Selected isotopes

                  CAPTION: Main article: Isotopes of xenon

                         iso     NA    half-life     DM   DE ( MeV)   DP
                        ^124Xe 0.1%   1.1×10^17 y  ε ε    no data   ^124Te
                        ^125Xe syn    16.9 h       ε      1.652     ^125I
                        ^126Xe 0.09%  Xe is stable with 72 neutrons
                        ^127Xe syn    36.4 d       ε      0.662     ^127I
                        ^128Xe 1.91%  Xe is stable with 74 neutrons
                        ^129Xe 26.4%  Xe is stable with 75 neutrons
                        ^130Xe 4.1%   Xe is stable with 76 neutrons
                        ^131Xe 21.29% Xe is stable with 77 neutrons
                        ^132Xe 26.9%  Xe is stable with 78 neutrons
                        ^133Xe syn    5.243 d      Beta^- 0.427     ^133Cs
                        ^134Xe 10.4%  Xe is stable with 80 neutrons
                        ^135Xe syn    9.10 h       Beta^- 1.16      ^135Cs
                        ^136Xe 8.9%   2.36×10^21 y Beta^- no data   ^136Ba

                                                                References

   Xenon ( IPA: /ˈzɛnɒn, ˈziːnɒn/) is a chemical element in the periodic
   table that has the symbol Xe and atomic number 54. A colorless, heavy,
   odorless noble gas, xenon occurs in the earth's atmosphere in trace
   amounts and was part of the first noble gas compound synthesized.

Notable characteristics

   Xenon is a member of the zero- valence elements that are called noble
   or inert gases, however, "inert" is not a completely accurate
   description of this chemical series since some noble gas compounds have
   been synthesized. In a gas filled tube, xenon emits a blue glow when
   the gas is excited by electrical discharge. Using tens of gigapascals
   of pressure, xenon has been forced into a metallic phase. Xenon can
   also form clathrates with water when atoms of it are trapped in a
   lattice of the water molecules.

Applications

   Xenon in shaped Geissler tubes.
   Enlarge
   Xenon in shaped Geissler tubes.

   This gas is most widely and most famously used in light-emitting
   devices called Xenon flash lamps, which are used in photographic
   flashes, stroboscopic lamps, to excite the active medium in lasers
   which then generate coherent light, to produce laser power for inertial
   confinement fusion, in bactericidal lamps (rarely), and in certain
   dermatological uses. Continuous, short-arc, high pressure Xenon arc
   lamps have a colour temperature closely approximating noon sunlight and
   are used in solar simulators, some projection systems, automotive HID
   headlights and other specialized uses. They are an excellent source of
   short wavelength ultraviolet light and they have intense emissions in
   the near infrared, which are used in some night vision systems. Other
   uses of Xenon:
     * Has been used as a general anaesthetic, though the cost is
       prohibitive.
     * In nuclear energy applications it is used in bubble chambers,
       probes, and in other areas where a high molecular weight and inert
       nature is a desirable quality.
     * Perxenates are used as oxidizing agents in analytical chemistry.
     * The isotope Xe-133 is useful as a radioisotope.
     * Hyperpolarized MRI of the lungs and other tissues using ^129Xe.
     * Preferred fuel for Ion propulsion because of high molecular weight,
       ease of ionization, store as a liquid at near room temperature (but
       at high pressure) yet easily converts back into a gas to fuel the
       engine, inert nature makes it environmentally friendly and less
       corrosive to an ion engine than other fuels such as mercury or
       cesium. Europe's SMART-1 spacecraft utilized Xenon in its engines.
     * Is commonly used in protein crystallography. Applied at high
       pressure (~600 psi) to a protein crystal, xenon atoms bind in
       predominantly hydrophobic cavities, often creating a high quality,
       isomorphous, heavy-atom derivative.

History

   Xenon ( Greek ξένος meaning "stranger") was discovered in England by
   William Ramsay and Morris Travers on July 12, 1898, shortly after their
   discovery of the elements krypton and neon. They found it in the
   residue left over from evaporating components of liquid air.

Occurrence

   Xenon is a trace gas in Earth's atmosphere, occurring in one part in
   twenty million. The element is obtained commercially through extraction
   from the residues of liquefied air. This noble gas is naturally found
   in gases emitted from some mineral springs. Xe-133 and Xe-135 are
   synthesized by neutron irradiation within air-cooled nuclear reactors.

Extraction

   Like the noble gas krypton , xenon can also be extracted by fractional
   distillation or liquefaction of liquid air and by selective adsorption
   on activated carbon.

Compounds

   Xenon tetrafluoride
   Enlarge
   Xenon tetrafluoride

   Xenon and the other noble gases had for a long time been considered to
   be completely chemically inert and not able to form compounds. However,
   in 1962 at the University of British Columbia, the first xenon
   compound, xenon hexafluoroplatinate, was synthesized. Now, many
   compounds of xenon are known, including xenon difluoride, xenon
   tetrafluoride, xenon hexafluoride, xenon tetroxide, xenon hydrate,
   xenon deuterate, and sodium perxenate. A highly explosive compound
   xenon trioxide has also been made. There are at least 80 xenon
   compounds in which fluorine or oxygen is bonded to xenon. Some
   compounds of xenon are colored but most are colorless.

   Recently at the University of Helsinki in Finland, a group of
   scientists (M. Räsänen et al.) prepared HXeH, HXeOH, and HXeCCH ( xenon
   dihydride, xenon hydride-hydroxide, and hydroxenoacetylene). They are
   stable up to 40 K.
   XeF4 crystals. 1962.
   Enlarge
   XeF[4] crystals. 1962.

Isotopes

   Naturally occurring xenon is made of seven stable and two slightly
   radioactive isotopes. Beyond these stable forms, there are 20 unstable
   isotopes that have been studied. Xe-129 is produced by beta decay of
   I-129 ( half-life: 16 million years); Xe-131m, Xe-133, Xe-133m, and
   Xe-135 are some of the fission products of both U-235 and Pu-239, and
   therefore used as indicators of nuclear explosions.

   The artificial isotope Xe-135 is of considerable significance in the
   operation of nuclear fission reactors. Xe-135 has a huge cross section
   for thermal neutrons, 2.65x10^6 barns, so it acts as a neutron absorber
   or "poison" that can slow or stop the chain reaction after a period of
   operation. This was discovered in the earliest nuclear reactors built
   by the American Manhattan Project for plutonium production. Fortunately
   the designers had made provisions in the design to increase the
   reactor's reactivity (the number of neutrons per fission that go on to
   fission other atoms of nuclear fuel).

   Relatively high concentrations of radioactive xenon isotopes are also
   found emanating from nuclear reactors due to the release of this
   fission gas from cracked fuel rods or fissioning of uranium in cooling
   water. The concentrations of these isotopes are still usually low
   compared to naturally occurring radioactive noble gases such as Rn-222.

   Because xenon is a tracer for two parent isotopes, Xe isotope ratios in
   meteorites are a powerful tool for studying the formation of the solar
   system. The I-Xe method of dating gives the time elapsed between
   nucleosynthesis and the condensation of a solid object from the solar
   nebula. Xenon isotopes are also a powerful tool for understanding
   terrestrial differentiation. Excess Xe-129 found in carbon dioxide well
   gases from New Mexico was believed to be from the decay of
   mantle-derived gases soon after Earth's formation.

Precautions

   The gas can be safely kept in normal sealed glass containers at
   standard temperature and pressure. Xenon is non- toxic, but many of its
   compounds are toxic due to their strong oxidative properties.

   Because xenon is denser than air, the speed of sound in xenon is slower
   than that in air, and when inhaled, lowers the resonant frequencies of
   the vocal tract. This produces a characteristic lowered voice pitch,
   opposite the high-pitched voice caused by inhalation of helium. Like
   helium, xenon does not satisfy the body's need for oxygen and is a
   simple asphyxiant; consequently, many universities no longer allow the
   voice stunt as a general chemistry demonstration. As xenon is
   expensive, the gas sulfur hexafluoride, which is similar to xenon in
   molecular weight (146 vs 131), is generally used in this stunt,
   although it too is an asphyxiant.

   A myth exists that xenon is too heavy for the lungs to expel
   unassisted, and that after inhaling xenon, it is necessary to bend over
   completely at the waist to allow the excess gas to "spill" out of the
   body. In fact, the lungs mix gases very effectively and rapidly, such
   that xenon would be purged from the lungs within a breath or two. There
   is, however, a danger associated with any heavy gas in large
   quantities: it may sit invisibly in a container, and if a person enters
   a container filled with an odorless, colorless gas, they may find
   themselves breathing it unknowingly. Xenon is rarely used in large
   enough quantities for this to be a concern, though the potential for
   danger exists any time a tank or container of xenon is kept in an
   unventilated space.
   Retrieved from " http://en.wikipedia.org/wiki/Xenon"
   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.
