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] 3d10 4s2 4p6
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
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
Main article: Isotopes of krypton iso NA half-life DM DE ( MeV) DP 78Kr 0.35% 2.3×1020 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 2.29×105 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.

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.