Krypton
- For other uses, see Krypton (disambiguation).
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| Name, Symbol, Number | krypton, Kr, 36 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Chemical series | noble gases | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Group, Period, Block | 18, 4, p | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Appearance | colorless 
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| 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 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Heat of vaporization | 9.08 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Heat capacity | (25 °C) 20.786 J/(mol·K) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Atomic properties | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Crystal structure | cubic face centered | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Oxidation states | 2 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electronegativity | 3.00 (Pauling scale) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Ionization energies (more) |
1st: 1350.8 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2nd: 2350.4 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 3rd: 3565 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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·K) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Speed of sound | (gas, 23 °C) 220 m/s | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Speed of sound | (liquid) 1120 m/s | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| CAS registry number | 7439-90-9 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Notable isotopes | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Krypton (chemical symbol Kr, atomic number 36) is a colorless, odorless, tasteless noble gas. It occurs in trace amounts in the atmosphere and is isolated by fractionating liquefied air. 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. It is often used with other rare gases in fluorescent lamps.
Occurrence
The concentration of krypton in earth's atmosphere is about 1 part per million (ppm). It can be extracted from liquid air by the technique known as fractional distillation.[1]
History
Krypton (Greek κρυπτός, meaning "hidden") was discovered in Great Britain in 1898 by Sir William Ramsay and Morris Travers. They found it in the residue that remained after evaporating nearly all components of liquid air.
Metric role
In 1960, an international agreement defined the meter in terms of light emitted from a krypton isotope. This agreement replaced the longstanding standard meter located in Paris, which was a metal bar made of platinum-iridium alloy. (The bar was originally estimated to be one ten-millionth of a quadrant of the Earth's polar circumference.) Just 23 years later, the krypton-based standard was replaced by a measure of 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 meter as the distance that light travels in a vacuum during 1/299,792,458 seconds.
Notable characteristics
Its melting point is 156.6 degrees celcius, and its boiling point is 152.3 degrees celcius. The density of krypton is 3.73 grams per liter at STP.
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."
Isotopes
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. Kr-81 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 Kr-81 has therefore been used for dating old (50,000 - 800,000 year) groundwater.
Kr-85 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 Kr-85 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 Kr-85 is produced in the northern hemisphere, and north-south atmospheric mixing is relatively slow.
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 difluoride was reported in 1963. [2] 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 40K(M. Räsänen et al.). See http://pubs.acs.org/cen/80th/noblegases.html in its paragraph starting "Many recent findings".
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.
ReferencesISBN links support NWE through referral fees
- Los Alamos National Laboratory - Krypton
- USGS Periodic Table - Krypton
- "Chemical Elements: From Carbon to Krypton" By: David Newton & Lawrence W. Baker
- "Krypton 85: a Review of the Literature and an Analysis of Radiation Hazards" By: William P. Kirk
External links
Template:ChemicalSources
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