10 Radon Facts (Rn or Atomic Number 86)

Radon Facts
Radon (atomic number 86) is a colorless radioactive gas that is naturally present in air and water. Radon exposure is a leading cause of lung cancer.

Radon is a radioactive gaseous element with atomic number 86 and element symbol Rn. Here are 10 interesting radon facts, including its discovery, sources, and why it’s so dangerous.

  1. Radon is a colorless, odorless, and flavorless noble gas. There are 33 isotopes of radon, all radioactive. The most common isotope is Rn-226, which emits alpha particles and has a half-life of 1601 years. Radon occurs naturally as a decay product of radium, uranium, thorium, and other radioactive isotopes.
  2. Radon was one of the first radioactive elements to be discovered. The discoverer is a source of debate. Ernest Rutherford and Robert B. Owens noticed thorium emitted a radioactive gas, which Rutherford called “emanation.” That same year, Pierre and Marie Curie noted the gas emitted by radium remained radioactive for a month. While Rutherford and Owens may be credited with the element discovery, Rutherford gave credit to the Curies. German Friedrich E. Dorn described radon gas in 1900. He called it “radium emanation” because he obtained the gas from a radium sample. William Ramsay and Robert Gray first isolated radon in 1908. They named the element niton, from the Latin word nitens, which means “shining.” In 1923, the name changed to radon, after radium, one of its sources and the element involved in its discovery.
  3. The abundance of radon in the Earth’s crust is 4 x 10-13 milligrams per kilogram. The element always occurs in air and drinking water, but usually in extremely low concentrations. It’s mainly a problem in enclosed spaces, such basements and mines.
  4. 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 counters, 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 often be reduced easily and inexpensively once the threat is known.
  5. Radon gas is invisible, but when it 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. So, solid radon is a colorful and glows in the dark.
  6. Radon is a noble gas. Like helium and argon, it has a stable outer electron shell. It is monatomic and does not readily form chemical compounds. However, can react react with fluorine to form radon fluoride. Radon clathrates are also known. Radon is one of the densest gases and is the heaviest. Radon is 9 times heavier than air.
  7. 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 penetrates most materials and disperses readily from its source.
  8. Children face a higher risk from radon exposure than adults. Genetic damage is more serious in kids because cells are dividing for growth more than in adults.
  9. At one time, radon-rich spas were all the rage because people thought the radioactive gas might confer medical benefits. Radon naturally occurs in certain hot springs, such as those around Hot Springs, Arkansas. For at time, radon gas was a cancer treatment. Today, radon finds use as a radioactive label to study surface chemical reactions and to initiate reactions.
  10. The easiest way to obtain radon is to isolate it from air. Because radon is heavier than air, gas accumulates at the bottom of enclosed structures. Another way to get the element is from the gases emitted by a radium salt. Sparking the gas mixture reacts hydrogen and oxygen, removing them as water. Adsorption removes the carbon dioxide. Chilling the remaining gas freezes the radon, separating it from nitrogen.

Basic Radon Facts

  • Element Name: Radon
  • Element Symbol: Rn
  • Atomic Number: 86
  • Element Group: Group 18 (Noble Gas)
  • Period: Period 6
  • Electron Configuration: [Xe] 4f14 5d10 6s2 6p6
  • Appearance: Colorless Gas
  • Melting Point: 202 K ​(−71 °C, ​−96 °F)
  • Boiling Point:
  • Density (at STP): 9.73 g/L
  • Oxidation States: 0, +2, +6
  • Electronegativity: 2.2 (Pauling scale)
  • Crystal Structure: face-centered cubic (fcc)
  • Magnetic Ordering: non-magnetic
  • Discovery: Ernest Rutherford and Robert B. Owens (1899)
  • First Isolation: William Ramsay and Robert Whytlaw-Gray (1910)


  • Cohen B. L. (1995). “Test of the linear-no threshold theory of radiation carcinogenesis for inhaled radon decay products”. Health Physics. 68 (2): 157–74. doi:10.1097/00004032-199502000-00002
  • Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. ISBN 1439855110
  • Kusky, Timothy M. (2003). Geological Hazards: A Sourcebook. Greenwood Press. pp. 236–239. ISBN 9781573564694.