Radon is colorless and the most dense gas known. Chemically unreactive, it is classed as an inert gas in group 0 of the periodic table . Synthesis of radon fluoride has been reported.
Radon is highly radioactive and has a short half-life.
The chief use of radon is in the treatment of cancer by radiotherapy. All naturally occurring radon decays by the emission of alpha particles. Radon is produced by the disintegration of its precursors in minerals, from which it diffuses in small amounts. In homes and other buildings in some areas of the U.S., radon produced by the radioactive decay of uranium-238 present in soil and rock can reach levels regarded as dangerous, but the seriousness of the problem is unclear. Twenty isotopes of radon are known, but only three occur naturally.