Radon
Radon is a radioactive noble gas formed naturally by the decay of heavier elements in rocks and soil.
Radon is a naturally occurring radioactive gas that can accumulate indoors.
Explore Radon's atom- Atomic number
- 86
- Source isotope mass
- 222.01758 u
- Family
- Noble gas
- Period
- 6
- Group
- 18
- Standard state
- Gas
In everyday life
Building ventilation and radon testing help manage exposure in affected areas.
Something to remember
Radon arises in radioactive decay chains involving elements such as uranium.
Meet its electrons
[Xe] 6s2 4f14 5d10 6p6
Published neutral-atom ground-state configuration; excited atoms and ions can differ.
Electrons per shell: 2 · 8 · 18 · 32 · 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
Radon can appear in decay chains that begin with uranium in rocks and soils.
Meet Uranium (U)Properties and conditions
- Source isotope mass
- 222.01758 uPubChem value for an element without stable isotopes. This is not a standard atomic weight and may be rounded to an isotope mass number; uncertainty is not supplied. CIAAW assigns no standard atomic weight to this element. The PubChem isotope is not necessarily the longest-lived isotope.PubChem periodic table ↗ · 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
- 10.745 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
- Not reportedA dimensionless relative measure; values depend on the chosen scale. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Melting point
- 202 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
- 211.45 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
- 0.00973 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
- 1900PubChem 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
- 220 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 1 isotope of Rn
| Isotope | Relative atomic mass | Natural fraction | Half-life | Decay |
|---|---|---|---|---|
| Rn-222Reference isotope | 222.0175782(25) | Not tabulated | 3.8215 d (uncertainty 0.0002) | α=100 |
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.