Krypton
[Ar] 3d¹⁰ 4s² 4p⁶ · 2 · 8 · 18 · 8
A noble gas whose name means hidden: krypton lurked in the residue of distilled air after the main components were already known. For decades a krypton line defined the metre.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 36
- Atomic mass
- 83.798 а.е.м.
- Electron configuration
- [Ar] 3d¹⁰ 4s² 4p⁶
- Electrons per shell
- 2 · 8 · 18 · 8
- Block
- p-block
- Group
- Noble gases
- Period
- 4
- Electronegativity (Pauling)
- 3
- Electronegativity (Allen)
- 2.97
- Atomic radius
- 88 pm
- Covalent radius
- 116 pm
- Van der Waals radius
- 202 pm
- Ionisation energy 1
- 1 350.8 kJ/mol
- Ionisation energy 2
- 2 350.4 kJ/mol
- Ionisation energy 3
- 3 565 kJ/mol
- Electron affinity
- 0 kJ/mol
- Common oxidation states
- 0
- Oxidation states
- 0, +1, +2
Physical properties
- State at 25 °C
- gas
- Density
- 0.00375 g/cm³
- Melting point
- 115.78 K · -157.4 °C
- Boiling point
- 119.93 K · -153.2 °C
- Speed of sound
- 1 120 m/s
Thermal properties
- Heat of fusion
- 1.64 kJ/mol
- Heat of vaporisation
- 9.08 kJ/mol
- Specific heat capacity
- 0.248 J/(g·K)
- Thermal conductivity
- 0.00943 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- no data
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- face-centred cubic (fcc)
- Lattice constants
- a = 570.6 pm
Abundance
- In the crust
- 0.0001 mg/kg
- In the ocean
- 0.00021 mg/L
- In the universe
- 400 mg/kg
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 78Kr | 0.355 % | stable | — |
| 80Kr | 2.286 % | stable | — |
| 82Kr | 11.593 % | stable | — |
| 83Kr | 11.5 % | stable | — |
| 84Kr | 56.987 % | stable | — |
| 86Kr | 17.279 % | stable | — |
Krypton-85, half-life 10.8 years, is released by nuclear fuel reprocessing, and its atmospheric level is an indicator of such activity.
Discovery
- Year of discovery
- 1898
- Discovered by
- William Ramsay and Morris Travers
- Where
- England
- Origin of the name
- from Greek kryptos (hidden)
History
Ramsay and Travers found krypton in May 1898 by boiling off nearly all of a sample of liquid air and studying what remained. In that same year they also found neon and xenon.
Where it occurs
1 ppm of the atmosphere — extremely scarce. Part of Earth's krypton is radiogenic, from uranium fission in the crust.
How it is produced
From air, at the final stage of cryogenic separation. It is costly because the concentration is so tiny.
Role in living things
No biological role. Under pressure it is more narcotic than nitrogen.
Safety
Chemically inert and non-toxic; hazardous only as an oxygen displacer.
Uses
- Filling energy-saving lamps and high-grade double glazing
- Krypton fluoride excimer lasers for photolithography
- High-speed photography: krypton flash lamps
- Leak detection and tracing air movement in studies
Curiosities
- From 1960 to 1983 the metre was defined as 1 650 763.73 wavelengths of krypton-86's orange line.
- The name means hidden — krypton was hiding in the distillation residue.
- Krypton outperforms argon in double glazing, at a markedly higher price.
- Krypton compounds are few; the most stable is KrF₂, and only at low temperature.