Radon
. Radon, symbol Rn, colorless, odorless radioactive gaseous element that is the heaviest of the noble gases of the periodic table . The atomic number of radon is 86. Radon-222 was discovered in 1900 by the German chemist Friedrich Ernst Dorn. Radon was believed to be chemically inert. Since 1962, however, chemists have been able to make radon compounds. Radon-222, which is the most abundant isotope of radon, is formed by the radioactive decay of radium-226 (see Radioactivity ). Radon-222 has a half-life of 3.8 days, decaying by the emission of alpha particles into an isotope of the element polonium . Radon makes up most normal background radioactivity. This colorless gas forms from the decay of uranium and radium , elements that are naturally present in rock and soil. Radon can concentrate in basements and other unventilated indoor areas built into the soil. Indoor accumulations of radon pose a serious health hazard. When radon breaks down, it produces charged particles that adhere