Krypton

36

Kr

83.798(2)

  • Name: Krypton
  • Symbol: Kr
  • Atomic number: 36
  • Atomic weight: 83.798(2)
  • CAS Registry ID: 7439-90-9
  • Group name: Noble gas
  • Period number: 4
  • Block: p-block
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Description

Krypton is a noble gas that is colorless, tasteless, and odorless in its natural gaseous state. As a noble gas, krypton has low reactivity characteristics. Krypton has an atomic weight of 83.798, a melting point of - 251.25 °F, and a boiling point of - 244.12 °F. Some common uses of krypton include: as a component with argon for florescent lights, as a component in flash lamps for high speed photography, and a component in the krypton fluoride laser for nuclear fusion research.

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Isolation

Krypton is only present in nature in gaseous form. The only method that is used to isolate pure krypton is fractional distillation of the air.

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Krypton is present in the earth’s atmosphere at a concentration of approximately 1 ppm. Liquid air fractional distillation is used not only for krypton, but for other components in the air as well including other noble gases. The principle of fractional distillation separation uses the different boiling points of the elements in the air to separate them. Liquid air fractional distillation is not usually performed on a small scale laboratory basis; industrial distillation is the most common form of liquid air fractional distillation.

During the krypton isolation process, the air is fed into a distillation column on a continual basis. The different processes of heating, cooling, and condensing, using liquid outlets and chambers to capture the isolated elements is what separates all of the gases that are in the earth’s atmosphere. Isolated krypton is extracted out as a gas, and it is then stored in its pure form in pressurized cylinders.


General
Name Krypton
Symbol Kr
Number 36
Chemical series noble gases
Group 18
Period 4
Block p
Appearance colorless
Standard atomic weight 83.798(2)  g·mol−1
Electron configuration [Ar] 3d10 4s2 4p6
Electrons per shell 2, 8, 18, 8
Atomic properties
Crystal structure cubic face centered
Oxidation states 2
Electronegativity 3.00 (scale Pauling)
Ionization energies 1st:  1350.8  kJ·mol−1
(more) 2nd:  2350.4  kJ·mol−1
(more) 3rd:  3565  kJ·mol−1
Atomic radius
Atomic radius (calc.) 88  pm
Covalent radius 110  pm
Van der Waals radius 202 pm
Physical properties
Phase gas
Density (near r.t.) (0 °C, 101.325 kPa) 3.749 g/L
Liquid density at m.p.
Melting point 115.79 K (-157.36 °C, -251.25 °F)
Boiling point 119.93 K (-153.22 °C, -244.12 °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
Miscellaneous
Magnetic ordering nonmagnetic
Electrical resistivity
Thermal conductivity (300 K) 9.43 m W·m−1·K−1
Thermal expansion
Speed of sound (thin rod) (gas, 23 °C) 220 m/s
Young's modulus
Shear modulus
Bulk modulus
Poisson ratio
Mohs hardness
Vickers hardness
Brinell hardness
CAS registry number 7439-90-9

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