   #copyright

Krypton

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                36              bromine ← krypton → rubidium
                Ar
                ↑
                Kr
                ↓
                Xe

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                      Name, Symbol, Number krypton, Kr, 36
                                               Chemical series noble gases
                                             Group, Period, Block 18, 4, p
                                                      Appearance colorless
                                              Atomic mass 83.798 (2) g/mol
                               Electron configuration [Ar] 3d^10 4s^2 4p^6
                                           Electrons per shell 2, 8, 18, 8
                                                       Physical properties
                                                                 Phase gas
                                              Density (0 °C, 101.325 kPa)
                                                                 3.749 g/L
                                                   Melting point 115.79  K
                                              (-157.36 ° C, -251.25 ° F)
                                                    Boiling point 119.93 K
                                               (-153.22 ° C, -243.8 ° F)
                                         Critical point 209.41 K, 5.50 MPa
                                          Heat of fusion 1.64 kJ·mol^−1
                                    Heat of vaporization 9.08 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 59 65 74  84   99   120

                                                         Atomic properties
                                     Crystal structure cubic face centered
                                                        Oxidation states 2
                                    Electronegativity 3.00 (Pauling scale)
                                                       Ionization energies
                                          ( more) 1st: 1350.8 kJ·mol^−1
                                                  2nd: 2350.4 kJ·mol^−1
                                                    3rd: 3565 kJ·mol^−1
                                               Atomic radius (calc.) 88 pm
                                                    Covalent radius 110 pm
                                               Van der Waals radius 202 pm
                                                             Miscellaneous
                                             Magnetic ordering nonmagnetic
                      Thermal conductivity (300 K) 9.43 mW·m^−1·K^−1
                                      Speed of sound (gas, 23 °C) 220 m/s
                                          Speed of sound (liquid) 1120 m/s
                                             CAS registry number 7439-90-9
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of krypton

                              iso   NA    half-life  DM   DE ( MeV)   DP
                             ^78Kr 0.35% 2.3×10^20 y ε ε -           ^78Se
                             ^79Kr syn   35.04 h     ε   -           ^79Br
                                                     β^+ 0.604       ^79Br
                                                     γ   0.26, 0.39,
                                                         0.60        -
                             ^80Kr 2.25% Kr is stable with 44 neutrons
                             ^81Kr syn   2.29×10^5 y ε   -           ^81Br
                                                     γ   0.281       -
                             ^82Kr 11.6% Kr is stable with 46 neutrons
                             ^83Kr 11.5% Kr is stable with 47 neutrons
                             ^84Kr 57%   Kr is stable with 48 neutrons
                             ^85Kr syn   10.756 y    β^- 0.687       ^85Rb
                             ^86Kr 17.3% Kr is stable with 50 neutrons

                                                                References

   Krypton ( IPA: /ˈkrɪptən/ or /ˈkrɪptan/) is a chemical element with the
   symbol Kr and atomic number 36. A colorless, odorless, tasteless noble
   gas, krypton occurs in trace amounts in the atmosphere, is isolated by
   fractionating liquefied air, and is often used with other rare gases in
   fluorescent lamps. Krypton is inert for most practical purposes but it
   is known to form compounds with fluorine. Krypton can also form
   clathrates with water when atoms of it are trapped in a lattice of the
   water molecules.

Notable characteristics

   Image of a krypton filled discharge tube shaped like the element's
   atomic symbol.
   Enlarge
   Image of a krypton filled discharge tube shaped like the element's
   atomic symbol.

   Krypton, a noble gas due to its very low chemical reactivity, is
   characterized by a brilliant green and orange spectral signature. It is
   one of the products of uranium fission. Solidified krypton is white and
   crystalline with a face-centered cubic crystal structure which is a
   common property of all "rare gases".

History

   Krypton ( Greek κρυπτός meaning "hidden") was discovered in Great
   Britain, 1898 by Sir William Ramsay and Morris Travers in residue left
   from evaporating nearly all components of liquid air.

Metric role

   In 1960 an international agreement defined the metre in terms of light
   emitted from a krypton isotope. This agreement replaced the
   longstanding standard metre located in Paris which was a metal bar made
   of a platinum-iridium alloy (the bar was originally estimated to be one
   ten millionth of a quadrant of the earth's polar circumference). But
   only 23 years later, the Krypton-based standard was replaced itself by
   the speed of light—the most reliable constant in the universe. In
   October 1983 the Bureau International des Poids et Mesures
   (International Bureau of Weights and Measures) defined the metre as the
   distance that light travels in a vacuum during 1/299,792,458 s.

Occurrence

   The concentration of krypton in earth's atmosphere is about 1 ppm. It
   can be extracted from liquid air by fractional distillation.

Compounds

   Like the other noble gases, krypton is widely considered to be
   chemically inert. Following the first successful synthesis of xenon
   compounds in 1962, synthesis of krypton di fluoride was reported in
   1963. Other fluorides and a salt of a krypton oxoacid have also been
   found. ArKr+ and KrH+ molecule- ions have been investigated and there
   is evidence for KrXe or KrXe+.

   At the University of Helsinki in Finland, HKrCN and HKrCCH (krypton
   hydride-cyanide and hydrokryptoacetylene) were synthesized and
   determined to be stable up to 40 K(M. Räsänen et al.). See
   http://pubs.acs.org/cen/80th/noblegases.html in its paragraph starting
   "Many recent findings".

Isotopes

   There are 32 known isotopes of krypton. Naturally occurring krypton is
   made of five stable and one slightly radioactive isotope. Krypton's
   spectral signature is easily produced with some very sharp lines. ^81Kr
   is the product of atmospheric reactions with the other naturally
   occurring isotopes of krypton. It is radioactive with a half-life of
   250,000 years. Like xenon, krypton is highly volatile when it is near
   surface waters and ^81Kr has therefore been used for dating old (50,000
   - 800,000 year) groundwater. ^85Kr is an inert radioactive noble gas
   with a half-life of 10.76 years, that is produced by fission of uranium
   and plutonium. Sources have included nuclear bomb testing, nuclear
   reactors, and the release of ^85Kr during the reprocessing of fuel rods
   from nuclear reactors. A strong gradient exists between the northern
   and southern hemispheres where concentrations at the North Pole are
   approximately 30% higher than the South Pole due to the fact that most
   ^85Kr is produced in the northern hemisphere, and north-south
   atmospheric mixing is relatively slow.

Krypton fluoride laser

   One major use of krypton is the krypton fluoride laser. Certain amounts
   of energy are added to force krypton gas to react with fluorine gas to
   become KrF excited state complex.

   The compound will decompose once the energy supply stops. During the
   decomposition process, the excess energy stored in the excited state
   complex will be emitted in the form of strong ultraviolet laser
   radiation.
   Retrieved from " http://en.wikipedia.org/wiki/Krypton"
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   with only minor checks and changes (see www.wikipedia.org for details
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