Krypton
Krypton is a colourless noble gas present in very small amounts in the atmosphere.
Krypton lights specialised lamps and has played a part in precision measurement.
Explore Krypton's atom- Atomic number
- 36
- Standard atomic weight
- 83.798(2)
- Family
- Noble gas
- Period
- 4
- Group
- 18
- Standard state
- Gas
In everyday life
Some photographic flash lamps and lighting systems use krypton.
Something to remember
A krypton spectral line once served as the basis for the definition of the metre.
Meet its electrons
[Ar] 4s2 3d10 4p6
Published neutral-atom ground-state configuration; excited atoms and ions can differ.
Electrons per shell: 2 · 8 · 18 · 8.
The playground shows an illustrative shell model. Real electrons are described by quantum orbitals, rather than tiny planets traveling along fixed paths.
A connection to explore
Krypton and xenon are heavier noble gases that can form some compounds.
Meet Xenon (Xe)Properties and conditions
- Standard atomic weight
- 83.798(2)CIAAW 2024 standard atomic weight (dimensionless). Parentheses give uncertainty in the last quoted digits. Source flags: g m.CIAAW standard atomic weights ↗ · Retrieved 2026-10-15
- Standard state
- GasPubChem classification, including explicit predictions where stated. Reference temperature and pressure are not supplied in the table.PubChem periodic table ↗ · Retrieved 2026-10-15
- First ionisation energy
- 14.000 eVEnergy to remove the first electron from an isolated neutral gas-phase atom. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Electronegativity
- 3 Pauling scaleA dimensionless relative measure; values depend on the chosen scale. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Melting point
- 115.79 KPubChem reported value. Pressure, allotrope and measurement uncertainty are not specified in the table; consult the cited source.PubChem periodic table ↗ · Retrieved 2026-10-15
- Boiling point
- 119.93 KPubChem reported value. Pressure and measurement uncertainty are not specified in the table; consult the cited source.PubChem periodic table ↗ · Retrieved 2026-10-15
- Density
- 0.003733 g/cm³PubChem reported value. Temperature, pressure, allotrope and measurement uncertainty are not specified in the table; gas densities are especially condition-dependent.PubChem periodic table ↗ · Retrieved 2026-10-15
- Oxidation states
- 0Selected PubChem oxidation states; formal electron bookkeeping, not a list of stable free-ion charges or every possible compound.PubChem periodic table ↗ · Retrieved 2026-10-15
- Discovery
- 1898PubChem discovery attribution. Ancient knowledge and competing priority claims cannot always be represented by a single year.PubChem periodic table ↗ · Retrieved 2026-10-15
- Atomic radius
- 202 pmPubChem tabulated radius. Radius definitions depend on bonding and convention; measurement definition and uncertainty are not supplied in this table.PubChem periodic table ↗ · Retrieved 2026-10-15
- Electron affinity
- Not reportedPubChem reported gas-phase electron affinity. Sign conventions and electronic states matter; uncertainty is not supplied in this table.PubChem periodic table ↗ · Retrieved 2026-10-15
Isotopes, abundance and decay
Isotopes share a proton count but have different neutron counts. This selection includes naturally tabulated compositions and a reference isotope for other elements. It is not a list of every known isotope.
Explore 6 isotopes of Kr
| Isotope | Relative atomic mass | Natural fraction | Half-life | Decay |
|---|---|---|---|---|
| Kr-78 | 77.92036494(76) | 0.00355(3) | No decay observed | ;2β+ ? |
| Kr-80 | 79.91637808(75) | 0.02286(10) | No decay observed | No decay tabulated |
| Kr-82 | 81.91348273(94) | 0.11593(31) | No decay observed | No decay tabulated |
| Kr-83 | 82.91412716(32) | 0.11500(19) | No decay observed | No decay tabulated |
| Kr-84 | 83.9114977282(44) | 0.56987(15) | No decay observed | No decay tabulated |
| Kr-86 | 85.9106106269(41) | 0.17279(41) | No decay observed | ;2β− ? |
Fractions use NIST’s terrestrial isotopic compositions, which can vary by sample. Parentheses denote uncertainty in the last digits. Half-lives and decay branches use NUBASE2020; # marks estimates, >/< mark limits. “No decay observed” follows that evaluation and does not prove permanent stability. Decay branch intensities are percentages; SF means spontaneous fission, EC electron capture, IT an isomeric transition.
Follow the science
Use these original references to explore the data and context. Atomic weights can vary with isotope composition; values for elements without stable isotopes may describe a representative isotope rather than a standard atomic weight.