Radon (Rn)

Radon (symbol Rn) is the chemical element with atomic number 86: a noble gas, radioactive, with an atomic mass of 222 u. Discovered in 1899 (Ernest Rutherford and Robert B. Owens).

Radon is a radioactive noble gas, colorless and odorless, produced by the decay of uranium naturally present in the ground. It builds up in poorly ventilated basements and ground floors, especially in granite regions. After tobacco, it is the leading cause of lung cancer, responsible for about 3,000 deaths a year in France.

Key facts

Atomic number: 86
Symbol: Rn
French name: Radon
Atomic mass: 222 u
Molar mass: [222] g/mol
Family: Noble gases
Position: period 6, group 18, p-block
State at 0 °C: Gas
Melting point: -71.1 °C
Boiling point: -61.6 °C
Density: 0.00973 g/cm³
Electronegativity (Pauling): 2.2
First ionization energy: 1,037 kJ/mol
Atomic radius: 120 pm
Electron configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶
Abundance in Earth's crust: 0 ppm (88th most abundant element)
Radioactive: yes
Discovery: 1899, Ernest Rutherford and Robert B. Owens

Origin of the name

From radium, from which it emanates.

What does radon look like?

A colorless, odorless gas, about eight times denser than air. Cooled until solid, it gives off a yellow, then orange glow caused by its radioactivity.

Where is radon found?

It is constantly produced in rocks and soils containing uranium and radium, especially granites. In France, Brittany, the Massif Central, Corsica and the Vosges are particularly affected.

Natural sources

Decay of uranium in the soil
Decay of radium in granites
Groundwater and hot springs

How is radon produced?

It is not produced industrially. In the lab it can be collected from a radium source, which gives it off continuously.

What is radon used for?

Tracer for studying groundwater and air masses.
Research on earthquake precursors.
Old-fashioned radiotherapy (radon “seeds”) and controversial spa cures.

In everyday life

The cellar or basement of a house in granite country
A home radon detector
A radioactive spa (Bad Gastein, Jáchymov)

Role in living things

No biological role. When inhaled, it decays into solid radioactive daughters (polonium, lead) that lodge in the airways and irradiate the cells.

Hazards of radon

A known human carcinogen. The risk is multiplied in smokers. France has set a reference level of 300 becquerels per cubic meter of indoor air; airing rooms regularly and sealing floors greatly reduces exposure.

Cosmic origin

None of it survives from the formation of the Solar System: it is constantly being created by the radioactive decay of uranium and thorium.

History of radon

In 1899 Ernest Rutherford and Robert Owens noticed that thorium gave off a radioactive “emanation”; in 1900 the German Friedrich Ernst Dorn saw the same thing with radium. William Ramsay and Robert Whytlaw-Gray isolated the gas in 1910 and measured its density. The name radon was adopted in 1923.

Did you know?

In 1984, American Stanley Watras set off the radiation alarms on his way into… his nuclear power plant: the contamination came from the radon in his house.
It is the densest naturally occurring gaseous element: about 9.7 grams per liter.
Radon-222 has a half-life of only 3.8 days, but it is constantly replenished by uranium in the soil.

Isotopes of radon

Radon has no stable isotopes: it is constantly being born from the uranium and thorium in rocks. Radon-222, which builds up in poorly ventilated homes, is the second leading cause of lung cancer after smoking.

radon-211: radioactive, half-life 14.6 h
radon-219: radioactive, half-life 3.96 s. Born from the uranium-235 chain, it was once called “actinon.”
radon-220: radioactive, half-life 55.6 s. Born from the thorium chain, it was once called “thoron.”
radon-222: radioactive, half-life 3.82 days. A natural radioactive gas seeping up from granite bedrock, monitored in homes; it also helps scientists study earthquakes and groundwater.

Related elements

Same family (noble gases): Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe).

Same column (group 18): Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), Oganesson (Og).