Radon
This article is about the chemical element radon. For other meanings, see Radon (disambiguation).
Radon [ˈʁaːdɔn], also: [ʁaˈdoːn] (like radium because of its radioactivity from Latin radius "ray") is a radioactive chemical element with the element symbol Rn and atomic number 86. In the periodic table, it is in the 8th main group, or the 18th IUPAC group, and thus belongs to the noble gases (hence the ending -on as an analogy).
All isotopes of radon are radioactive. The most stable - and also naturally occurring - isotope is 222Rn with a half-life of 3.8 days; it is formed as a decay product from the radium isotope 226Ra. Two other natural isotopes, 219Rn and 220Rn, are sometimes referred to by their historical trivial names actinon (An) and thoron (Tn), respectively. The fourth natural isotope, 218Rn, plays no role in terms of quantity compared to the three previously mentioned.
Since radon can accumulate in houses (unlike in the natural environment) in poorly ventilated rooms, it poses a health hazard and a significant radon exposure. The main source of danger is ultimately not radon itself, but its decay products, with polonium isotopes contributing most to alpha radiation exposure. Radon accounts for by far the largest share of total radiation on the earth's surface (average effective dose per person in Germany: about 1.1 mSv/year), followed by direct terrestrial radiation with about 0.4 mSv/year, direct cosmic radiation and radioactive substances naturally occurring in food with about 0.3 mSv/year each.
History
Radon was discovered in 1900 by Friedrich Ernst Dorn.
In 1908, William Ramsay and Robert Whytlaw-Gray isolated a sufficient quantity of the gas to determine its density. Because it gave off light in the dark, they named it niton, after the Latin word nitens "luminous". In 1923, the terms radium emanation and niton were replaced by the term radon.
Properties
Like all noble gases, radon is almost chemically unreactive; with fluorine it reacts to form radon difluoride, whether compounds with oxygen have been observed is disputed. Under normal conditions, radon gas is colorless, odorless, tasteless; when cooled below its melting point, it becomes bright yellow to orange. As a filling in gas discharge tubes, radon produces red light. It is also by far the densest elemental gas, at 9.73 kg-m-3, except for the exotically rare astatine and hot diatomic iodine vapor.
Like its lighter group homologue xenon, radon is capable of forming true compounds. These can be expected to be more stable and diverse than those of xenon. The study of radon chemistry is greatly hindered by the high specific activity of radon, because the high-energy radiation leads to self-decomposition (autoradiolysis) of the compounds. Therefore, chemistry with ponderable amounts of these substances is not possible. Ab-initio and Dirac-Hartree-Fock calculations describe some properties of the not yet synthesized radon hexafluoride (RnF6).
As a radioactive gas with a very high density, radon can accumulate in physiologically significant quantities in buildings, especially in basements and the lower floors. In recent measurements, larger amounts of radon were also found on the upper floors of buildings where building materials such as unburnt clay were used.
The solubility of the isotope Rn-222 in water at 20 °C and 101.325 kPa is 259 ml/l.
