36
  Kr  
83.800000
Krypton

Name: Krypton
Symbol: Kr
Atomic Number: 36
Atomic Weight: 83.800000
Family: Noble Gases
CAS RN: 7439-90-9
Description: A colorless inert gas.
State (25C): Gas
Oxidation states: 0

Molar Volume: 32.2 cm3/mole
Valence Electrons: 4p6

Boiling Point:  119.95K, -153.2C, -243.8F
Melting Point:
115.93K, -157.22C, -251F
Electrons Energy Level: 2, 8, 18, 8
Isotopes: 20 + 6 Stable
Heat of Vaporization: 9.029 kJ/mol
Heat of Fusion: 1.638 kJ/mol
Density: 3.75 g/L @ 273K & 1atm
Specific Heat: 0.248 J/gK
Atomic Radius: 1.03
Ionic Radius: unknown
Electronegativity: N/A (Pauling); 2.94 (Allrod Rochow)
Krypton (Greek, ???pt?? meaning "hidden") is neither green nor a solid material that can defeat Superman.  It was discovered in Great Britain, 1898 by Sir William Ramsay and Morris Travers in residue left from evaporating nearly all components of liquid air.  It ranks sixth in abundance in the atmosphere. Krypton gas is used in various kinds of lights, from small bright flashlight bulbs to special strobe lights for airport runways.

Krypton is characterized by a brilliant red 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".

As with the other noble gases, krypton is isolated from the air by liquefaction.

In 1960 an international agreement defined the meter in terms of light emitted from a krypton isotope.  One of the naturally occurring non-radioactive isotopes of krypton, Kr-86 (17.3%) was used as the basis for the international definition of the meter.  One meter was 1,650,762.73 wavelengths of the red-orange spectral line of krypton-86.  This agreement replaced the longstanding standard meter 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 meter as the distance that light travels in a vacuum during 1/299,792,458 seconds.

2
He
4.002
10
Ne
20.17
18
Ar
39.94
36
Kr
83.80
54
Xe
131.3
86
Rn
222.0
118
Uuo
293.0

1s2 2s2p6 3s2p6d10 4s2p6

Occurrence

The concentration of krypton in earth's atmosphere is about 1 ppm.  It can be extracted from liquid air by fractional distillation.  Once thought to be completely inert, krypton is known to form a few compounds. Krypton difluoride (KrF2) is the easiest krypton compound to make and gram amounts of it have been produced.

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.  Other fluorides and a salt of a krypton oxoacid have also been found.  ArK+ 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 40oK.  

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6

Isotopes

There are 20 known isotopes of krypton. Naturally occurring krypton is made of six 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.

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Isotope Atomic Mass Half-Life
Kr69 68.965  
Kr70 69.956  
Kr71 70.951 64 ms
Kr72 71.942 17.2 seconds
Kr73 72.939 27 seconds
Kr74 73.9333 11.5 minutes
Kr75 74.931 4.3 minutes
Kr76 75.9259 14.8 hours
Kr77 76.9247 74.4 minutes
Kr78 77.9204 Stable
Kr79 78.9201 35.04 hours
Kr80 79.9164 Stable
Kr81 80.9166 229000 years
Kr82 81.9135 Stable
Kr83 82.9141 Stable
Kr84 83.9115 Stable
Kr85 84.9125 10.756 years
Kr86 85.9106 Stable
Kr87 86.9134 76.3 minutes
Kr88 87.9144 2.84 hours
Kr89 88.9176 3.15 minutes
Kr90 89.9195 32.32 seconds
Kr91 90.9234 8.57 seconds
Kr92 91.9262 1.840 seconds
Kr93 92.931 1.286 seconds
Kr94 93.934 0.2 seconds
Kr95 94.94 0.78 seconds
Kr96 95.943  
Kr97 96.949 >150 ns

Uses

The high cost of obtaining krypton from the air has limited its practical applications. Krypton is used in some types of photographic flashes used in high speed photography. Some fluorescent light bulbs are filled with a mixture of krypton and argon gases. Krypton gas is also combined with other gases to make luminous signs that glow with a greenish-yellow light. In 1960, the length of the meter was defined in terms of the orange-red spectral line of krypton-86, an isotope of krypton. Argon gases are mixed with Krypton to create a special kind of fluorescent light bulb.

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.


atom.gif (700 bytes)

Krypton Data

 

Atomic Structure

Atomic Radius (): 1.03
Atomic Volume cm3/mol : 38.9cm3/mol
Covalent Radius: 1.12
Crystal Structure: Cubic face centered
Ionic Radius: unknown

Chemical Properties

Electrochemical Equivalents: unknown
Electron Work Function: unknown
Electronegativity: N/A (Pauling); 2.94 (Allrod Rochow)
Heat of Fusion: 1.638 kJ/mol
Incompatibilities: unknown
First Ionization Potential: 13.999
Second Ionization Potential: 24.359
Third Ionization Potential: 36.95
Valence Electron Potential: unknown
Ionization Energy (eV): 14.000 eV

Physical Properties

Atomic Mass Average: 83.8
Boiling Point: 119.95K, -153.2C, -243.8F
Melting Point: 115.93K, -157.22C, -251F
Heat of Vaporization: 9.029 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: N/A
Electrical Conductivity: unknown
Thermal Conductivity: 0.0000949 W/cmK
Density: 3.75 g/L @ 273K & 1atm
Enthalpy of Atomization: unknown
Enthalpy of Fusion: 1.64 kJ/mole
Enthalpy of Vaporization: 9.03 kJ/mole
Flammability Class: unknown
Molar Volume: 32.2 cm3/mole
Optical Refractive Index: 1.000427
Relative Gas Density (Air=1): unknown
Specific Heat: 0.248 J/gK
Vapor Pressure: unknown
Estimated Crustal Abundance: 110-4 milligrams per kilogram
Estimated Oceanic Abundance: 2.110-4 milligrams per liter


(Gr. kryptos, hidden) Discovered in 1898 by Ramsay and Travers in the residue left after liquid air had nearly boiled away. Krypton is present in the air to the extent of about 1 ppm. The atmosphere of Mars has been found to contain 0.3 ppm of krypton. It is one of the "noble" gases. It is characterized by its brilliant green and orange spectral lines. Naturally occurring krypton contains six stable isotopes. Seventeen other unstable isotopes are now recognized. The spectral lines of krypton are easily produced and some are very sharp. In 1960 it was internationally agreed that the fundamental unit of length, the meter, should be defined in terms of the orange-red spectral line of 86Kr. This replaced the standard meter of Paris, which was defined in terms of a bar made of a platinum-iridium alloy. In October 1983 the meter, which originally was defined as being one ten millionth of a quadrant of the earth's polar circumference, was again redefined by the International Bureau of Weights and Measures as being the length of a path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second. Solid krypton is a white crystalline substance with a face-centered cubic structure which is common to all the "rare gases." While krypton is generally thought of as a rare gas that normally does not combine with other elements to form compounds, it now appears that the existence of some krypton compounds is established. Krypton difluoride has been prepared in gram quantities and can be made by several methods. A higher fluoride of krypton and a salt of an oxyacid of krypton also have been reported. Molecule-ions of ArKr+ and KrH+ have been identified and investigated, and evidence is provided for the formation of KrXe or KrXe+. Krypton clathrates have been prepared with hydroquinone and phenol. 85Kr has found recent application in chemical analysis. By imbedding the isotope in various solids, kryptonates are formed. The activity of these kryptonates is sensitive to chemical reactions at the surface. Estimates of the concentration of reactants are therefore made possible. Krypton is used in certain photographic flash lamps for high-speed photography. Uses thus far have been limited because of its high cost. Krypton gas presently costs about $30/l.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond