Radon
Radioactive noble gas, colorless and odorless, second leading cause of lung cancer.
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Radon is a chemical element with symbol Rn and atomic number 86, classified as a radioactive noble gas that is both colorless and odorless. Among its three naturally occurring isotopes, only radon-222 possesses a half-life (3.825 days) long enough to escape from the soil and rock where it forms. Radon isotopes arise directly from the decay of radium isotopes.
The instability of radon-222, the element’s most stable isotope, makes radon one of the rarest elements, yet it will persist on Earth for billions of years because it is continuously produced in the decay chains of uranium and thorium, both abundant radioactive elements with half-lives of several billion years. Radon’s decay generates many short-lived nuclides, known as radon daughters, which ultimately become stable lead isotopes. Radon-222 occurs significantly in the uranium decay series, while minute amounts appear in the thorium series.
History and etymology
Discovered in 1899 by Ernest Rutherford and Robert B. Owens at McGill University, radon was the fifth radioactive element identified. Initially called “emanation,” the gas was observed during experiments with radium, thorium oxide, and actinium by Friedrich Ernst Dorn, Rutherford and Owens, and André-Louis Debierne, respectively; each emanation was thought to be a distinct substance: radon, thoron, and actinon. Sir William Ramsay and Robert Whytlaw-Gray isolated “radium emanation” in 1909, determining it belonged to the noble gas family. In 1911, the International Commission for Atomic Weights accepted the element, and in 1923, IUPAC adopted radon as the name for its most stable isotope, recognizing thoron and actinon as distinct isotopes.
Environmental radon commonly originates from uranium-containing minerals in the ground, and it can also occur in groundwater, including spring waters and hot springs. Permafrost thawing due to climate change may release trapped radon, and seismic events can release radon into groundwater and the atmosphere, prompting its study for earthquake prediction.
Testing for radon in buildings is possible, with mitigation techniques like sub-slab depressurization. Epidemiological studies link high radon concentrations to lung cancer; radon is a global indoor air contaminant. Denser than air, it accumulates in basements and crawlspaces.
Quick Facts
- Atomic number
- 86
- Discoverers
- Ernest Rutherford and Robert B. Owens
Facts from the source article.
Lore & Background
Radon was discovered in 1899 by Ernest Rutherford and Robert B. Owens at McGill University in Montreal, and was the fifth radioactive element to be discovered. First known as 'emanation', the radioactive gas was identified during experiments with radium, thorium oxide, and actinium by Friedrich Ernst Dorn, Rutherford and Owens, and André-Louis Debierne, respectively, and each element's emanation was considered to be a separate substance: radon, thoron, and actinon. Sir William Ramsay and Robert Whytlaw-Gray considered that the radioactive emanations may contain a new element of the noble gas family, and isolated 'radium emanation' in 1909 to determine its properties. In 1911, the element Ramsay and Whytlaw-Gray isolated was accepted by the International Commission for Atomic Weights, and in 1923, the International Committee for Chemical Elements and the International Union of Pure and Applied Chemistry (IUPAC) chose radon as the accepted name for the element's most stable isotope, 222Rn; thoron and actinon were also recognized by IUPAC as distinct isotopes of the element.
Reader's Guide
Radon is a member of the zero-valence elements called noble gases, and is chemically not very reactive. It is inert to most common chemical reactions, such as combustion. Radon can be oxidized by powerful oxidizing agents such as fluorine, forming radon difluoride (RnF2).
Radon oxides are among the few other reported compounds; only the trioxide (RnO3) has been confirmed. Radon is denser than air, accumulating in basements and crawlspaces. Epidemiological studies have shown a clear association between breathing high concentrations of radon and incidence of lung cancer.
According to the United States Environmental Protection Agency (EPA), radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the United States. About 2,900 of these deaths occur among people who have never smoked. While radon is the second most frequent cause of lung cancer, it is the number one cause among non-smokers, according to EPA policy-oriented estimates.
Frequently Asked Questions
Who is Radon?
Radon is a colorless, odorless noble gas with atomic number 86 and symbol Rn, sitting at the tail end of the periodic table's noble-gas column. It is a naturally occurring radioactive element that no human sense can detect, making it a truly invisible member of the element roster.
What is Radon known for?
Radon's defining trait is its radioactivity: its most stable isotope, Rn-222, decays with a half-life of roughly 3.8 days while emitting alpha particles. In practical terms, its role is as a natural indoor-air contaminant that seeps up through soil and bedrock into homes and workplaces.
How was Radon discovered?
In 1900, Ernest Rutherford and Robert B. Owens noticed a mysterious gaseous by-product being released from radium compounds and initially dubbed it 'radium emanation.' The substance was later recognized as a distinct element, given the name Radon, and assigned its own square on the periodic table.
Why is Radon so rare on Earth?
Every isotope of Radon is radioactive and decays within days to weeks, so no stable form ever accumulates in the crust. The most persistent isotope, Rn-222, lasts only about 3.8 days before transforming into polonium, meaning Radon exists in a constant, tiny cycle of creation and destruction.
Why is Radon a major health concern?
Radon is the second leading cause of lung cancer after cigarette smoking, because its short-lived decay products lodge in lung tissue and deliver concentrated alpha-radiation doses. Since the gas is invisible and odorless, people can inhale it for years without realizing, which is why indoor radon testing is widely recommended.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Radon (CC BY-SA 4.0).
- Word definitions: the Codexery glossary, each quoted from its Wikipedia article.
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