ElementsWhat is radon?
Radon is a radioactive gas without colour or smell. It seeps naturally from rocks and soil and can collect inside buildings, where breathing it for years raises the risk of lung cancer.
What is radon used for?
Very few uses today. Radon in homes is measured so that it can be reduced.
Where the name comes from
From radium, because it is given off when radium decays.
Key facts
- Symbol
- Rn
- Atomic number
- 86
- Atomic mass
- 222.01758 u
- Family
- Noble gas
- Period
- 6
- Group
- 18
- Block
- p
- State at room temperature
- Gas
- Melting point
- -71.1 °C (202 K, -96 °F)
- Boiling point
- -61.7 °C (211.45 K, -79 °F)
- Density
- 0.00973 g/cm³ (as a gas at 0 °C)
- Electrons per shell
- 2, 8, 18, 32, 18, 8
- Electron configuration
- [Xe]6s2 4f14 5d10 6p6
- Common oxidation states
- 0
- Electronegativity (Pauling)
- no value
- First ionisation energy
- 10.745 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 220 pm
- Discovered
- 1900
Place in the periodic table
Radon is element number 86. It sits in period 6 (row 6) of the periodic table, in group 18 (column 18), and belongs to the p-block. Just before it comes astatine (85), and just after it comes francium (87). In the same column, xenon is above it and oganesson is below it. Elements in one column tend to behave alike.
Family: Noble gases.
Physical properties
At room temperature radon is a gas. It melts at -71.1 °C and boils at -61.7 °C, so it stays liquid over a range of 9 degrees. One litre of the gas weighs about 9.73 grams at 0 °C and normal pressure. That is heavier than air, which weighs about 1.29 grams a litre.
Inside the atom
An atom of radon has 86 protons in its nucleus and, when neutral, 86 electrons around it. The electrons are arranged in 6 shells: 2, 8, 18, 32, 18, 8. The outermost shell holds 8 electrons. Written in full, the electron configuration is [Xe]6s2 4f14 5d10 6p6.
Removing one electron from an atom takes 10.745 electronvolts (about 1,037 kilojoules per mole). One mole of radon weighs 222.01758 grams, so a single gram contains about 2.71 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains radon with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.