K
- PDF / 176,672 Bytes
- 1 Pages / 595.276 x 841.89 pts (A4) Page_size
- 60 Downloads / 228 Views
KRYPTON Krypton was discovered in 1898 by W. Ramsay and M.W. Travers in the residue of liquid air. Its name comes from the Greek kryptos ='the hidden one'. Kr has the atomic number 36. It has 6 stable isotopes 78 Kr, 8 °Kr, 82 Kr, 83 Kr, 84 Kr and 86 Kr, with respective atomic masses of 77.920368, 79.913680, 81.913482, 82.914135, 83.911507 and 85.910616. Its atomic weight is 83.80 gjmol; melting point: 116.55 K; boiling point: 119.80 K. The atomic diameter is 3.58 A. Gas density is 3.733 kg/m 3 at 1 atm and 237.15 K. Krypton has the electron configuration 1s2 2s 2 p 6 3s 2 p 6 d 10 4s 2 p 6 and a first ionization potential of 13.999 eV. Its valence is usually 0, but 2, 4, 6 and 8 are observed. It forms the hydride ion KrH+, krypton difluoride KrF 2 and a hydroquinone clathrate [C 6 H 4 (0H) 2 h · 0.74Kr, which forms stable crystals (Cook, 1961). Dry air contains 1.14 X 10- 4 vol.% krypton with 78 KrjB 4 Kr, 8 °Kr/ 84 Kr, 82 Krj 84 Kr, 83 Kr/ 84 Kr and 86 Kr/ 84 Kr ratios of 0.006087, 0.03960, 0.20217, 0.20136 and 0.30524 respectively. Seventeen radioactive isotopes are known, 72 Kr- 77 Kr, 79 Kr, 81 Kr, 85 K, 87 Kr- 94 Kr with half-lives between 11.5 ms and 2.1 x 10 5 years. It is an uncolored, odorless and tasteless gas. Since 1960, the orange-red spectral line of 86 Kr has been used to define the standard meter: 1m= 1650 763.73 times the wavelength of the transition 5d 5 to 2p 10 under vacuum. It is commercially produced by liquefying air and used in incandescent lamps mixed with Ar and Xe, in fluorescent tubes and in arc flash lamps for illumination of airports. The narcotic effects of krypton-oxygen mixtures are only slight and have no clinical
application. The radioactive isotopes 85 Kr and 87 Kr with halflives of 10.72 years and 76.3 min were used for biological investigations. Kr is used together with other noble gases to determine paleotemperatures in ground water aquifers and allow observations of differences in temperature of several degrees (Stute et al., 1992). 83 Kr, 84 Kr and 86Xe isotopes were formed in nature by spontaneous fission of 238 U (Jc" = 1.55 x I 0- 9 a-\ Asr = 1.11 X 10- 16 a- 1 ), with a production rate which is 6.] times smaller than for spontaneous 136Xe (Eikenberg et al., 1993). The spontaneous fission Kr is used for the U-Kr dating method, which is less useful than the U-Xe method due the lower fission yield and the usually higher initial Kr abundance compared to Xe. For the same reason, krypton is much less important in geochemical investigations. Thomas Staudacher
Bibliography Cook G.A. (1961) Argon, helium and the rare gases, The Elements of the Helium Group, Vol!. New York: Interscience Publishers. Eikenberg, J., Signer, P. and Wieler, R. ( 1993) U-Xe, U-Kr, and U-Pb systematics for dating uranium minerals and investigations of the production of nucleogenic neon and argon. Geochim. Cosmochim. Acta, 57, 1053-69. Stute, M., Schlosser, P., Clark, J.F. and Broecker, W.S. (1992) Paleotemperatures in the southwestern United States derived from noble gases in ground water. Science, 25
Data Loading...
