10 Radon Facts (Rn or Atomic Number 86)

A Colorless Radioactive Gas

Radon on the periodic table

William Andrew / Getty Images

Radon is a natural radioactive element with the element symbol Rn and atomic number 86. Here are 10 radon facts. Knowing them could even save your life.

Fast Facts: Radon

  • Element Name: Radon
  • Element Symbol: Rn
  • Atomic Number: 86
  • Element Group: Group 18 (Noble Gas)
  • Period: Period 6
  • Appearance: Colorless Gas
  1. Radon is a colorless, odorless, and flavorless gas at ordinary temperature and pressure. Radon is radioactive and decays into other radioactive and toxic elements. Radon occurs in nature as the decay product of uranium, radium, thorium, and other radioactive elements. There are 33 known isotopes of radon. Rn-226 is the most common of these. It is an alpha emitter with a half-life of 1601 years. None of the isotopes of radon are stable.
  2. Radon is present in the Earth's crust at an abundance of 4 x10-13 milligrams per kilogram. It is always present outdoors and in drinking water from natural sources, but at a low level in open areas. It's mainly a problem in enclosed spaces, such as indoors or in a mine.
  3. The US EPA estimates the average indoor radon concentration is 1.3 picocuries per liter (pCi/L). It's estimated approximately 1 in 15 homes in the US has high radon, which is 4.0 pCi/L or higher. High radon levels been found in every state of the United States. Radon comes from the soil, water, and water supply. Some building materials also release radon, such as concrete, granite countertops, and wall boards. It's a myth that only older homes or ones of a certain design are susceptible to high radon levels, as the concentration depends on many factors. Because it is heavy, the gas does tend to accumulate in low-lying areas. Radon test kits can detect high levels of radon, which can generally be mitigated fairly easily and inexpensively once the threat is known.
  4. Radon is the second leading cause of lung cancer overall (after smoking) and the leading cause of lung cancer in non-smokers. Some studies link radon exposure to childhood leukemia. The element emits alpha particles, which are not able to penetrate skin, but can react with cells when the element is inhaled. Because it is monatomic, radon is able to penetrate most materials and disperses readily from its source.
  5. Some studies indicate children are at higher risk from radon exposure than adults. The most probable reason is that children's cell divide more often than those of adult, so genetic damage is more likely and has greater consequences. Partly, cells divide more rapidly because children have a higher metabolic rate, but it's also because they are growing.
  6. The element radon has gone by other names. It was one of the first radioactive elements that was discovered. Fredrich E. Dorn described radon gas in 1900. He called it "radium emanation" because the gas came from the radium sample he was studying. William Ramsay and Robert Gray first isolated radon in 1908. They named the element niton. In 1923, the name changed to radon, after radium, one of its sources and the element involved in its discovery.
  7. Radon is a noble gas, which means it has a stable outer electron shell. For this reason, radon does not readily form chemical compounds. The element is considered chemical inert and monatomic. However, it has been known to react with fluorine to form a fluoride. Radon clathrates are also known. Radon is one of the densest gases and is the heaviest. Radon is 9 times heavier than air.
  8. Although gaseous radon is invisible, when the element is cooled below its freezing point (−96 °F or −71 °C), it emits bright luminescence that changes from yellow to orange-red as the temperature is lowered.
  9. There are some practical uses of radon. At one time, the gas was used for radiotherapy cancer treatment. It used to be used in spas, when people thought it might confer medical benefits. The gas is present in some natural spas, such as the hot springs around Hot Springs, Arkansas. Now, radon is mainly used as a radioactive label to study surface chemical reactions and to initiate reactions.
  10. While radon is not considered a commercial product, it may be produced by isolating gases off of a radium salt. The gas mixture can then be sparked to combine hydrogen and oxygen, removing them as water. Carbon dioxide is removed by adsorption. Then, radon may be isolated from nitrogen by freezing out the radon.


  • Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.122. ISBN 1439855110
  • Kusky, Timothy M. (2003). Geological Hazards: A Sourcebook. Greenwood Press. pp. 236–239. ISBN 9781573564694.
mla apa chicago
Your Citation
Helmenstine, Anne Marie, Ph.D. "10 Radon Facts (Rn or Atomic Number 86)." ThoughtCo, Feb. 16, 2021, thoughtco.com/interesting-radon-element-facts-603364. Helmenstine, Anne Marie, Ph.D. (2021, February 16). 10 Radon Facts (Rn or Atomic Number 86). Retrieved from https://www.thoughtco.com/interesting-radon-element-facts-603364 Helmenstine, Anne Marie, Ph.D. "10 Radon Facts (Rn or Atomic Number 86)." ThoughtCo. https://www.thoughtco.com/interesting-radon-element-facts-603364 (accessed June 6, 2023).