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Krypton,  36Kr
General properties
Name, symbol Krypton, Kr
Appearance Colorless gas
Exhibits a whitish glow in a high electric field
Krypton in the periodic table


Atomic number 36
Standard atomic weight (Ar)
Group, block 18; p-block
Period period 4
Electron configuration [Ar] 3d10 4s2 4p6
per shell
2, 8, 18, 8
Physical properties
Phase Gas
Melting point 115.78 K ​(−157.37 °C, ​−251.27 °F)
Boiling point 119.93 K ​(−153.415 °C, ​−244.147 °F)
Density at  (0 °C and 101.325 kPa) 3.749 g/L
when liquid, at  2.413 g/cm3 b.p.
Triple point 115.775 K, ​73.53 kPa
Critical point 209.48 K, 5.525 MPa
Heat of fusion 1.64 kJ/mol
Heat of 9.08 kJ/mol
Molar heat capacity 20.95 J/(mol·K)
Atomic properties
Oxidation states 2, 1, 0 ​(rarely more than 0; unknown oxide)
Electronegativity Pauling scale: 3.0
energies 1st: 1350.8 kJ/mol
2nd: 2350.4 kJ/mol
3rd: 3565 kJ/mol
Covalent radius 116±4 pm
Van der Waals radius 202 pm
Crystal structure ​face-centered cubic (fcc)
Speed of sound gas (23 °C): 220 m/s
liquid: 1120 m/s
Thermal conductivity 9.43×10−3 W/(m·K)
Magnetic ordering Diamagnetic
CAS Registry Number 7439-90-9
Discovery and first isolation William Ramsay and Morris Travers (1898)
· references

Krypton is a chemical element with symbol Kr and atomic number 36. Along with xenon and radon, it is the only noble gas to form true chemical compounds.



Krypton is nonreactive to all chemicals but fluorine.

The reaction of krypton with fluorine gives krypton difluoride (KrF2). KrF2 is made by irradiating krypton with ultraviolet rays in a fluorine-argon gas mixture at -265 °C:

Kr + F2 → KrF2

Other compounds, such as krypton hydride (Kr(H2)4) are also known. All of these compounds are stable only at very low temperatures.

However, as krypton compounds can only be made with the super dangerous fluorine at very low temperatures and the relative high price of krypton, they have no useful application to the amateur chemist.


Krypton is a dense, colorless, odorless, non-flammable gas. At standard conditions, krypton has a density of 3.749 g/L being 3 times denser than air, while cryogenic krypton has a density of 2.413 g/cm3. Krypton has the second widest liquid phase range among the noble gasses (after radon), with a boiling point of −157.37 °C and a melting point of −153.415 °C.


Krypton is sold by various compressed gas companies, though it's quite expensive.

Certain gas discharge lamps contain krypton.


Krypton can be isolated from the fractional distillation of air, but this method requires processing extremely large amounts of air and is too expensive for the amateur chemist.


  • Gas discharge lamp
  • Element collection
  • Inert atmosphere (expensive)



Being a noble gas, krypton is non-toxic, though inhaling large amounts of krypton can lead to asphyxiation, as it displaces the air from lungs.


Krypton cylinders should be stored in dark places, away from any heat source and not in the basement.


Krypton can be safely released in the air.


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