Radon (Rn)


  • Symbol: Rn
  • Atomic Number: 86
  • Atomic Weight: [222]
  • Element Classification: Noble Gas
  • Discovered By: Friedrich Ernst Dorn
  • Discovery Date: 1900
  • Name Origin: Derived from radium; originally called “radium emanation”
  • Density(g/cc): 0.00973 (gas at 0°C, 1 atm)
  • Melting Point: -71°C
  • Boiling Point: -61.7°C
  • Appearance: Colorless gas under standard conditions
  • Atomic Radius(pm): Estimated to be about 120


Radon was discovered in 1900 by German physicist Friedrich Ernst Dorn, who observed it as a radioactive gas released from radium compounds. Dorn initially called it “radium emanation” because it was produced from radium. The element was later named “radon” to align with the naming convention of noble gases and to indicate its origin from radium decay.

Relation to Other Elements

Radon is a member of the noble gases, which also includes helium, neon, argon, krypton, and xenon. As the heaviest naturally occurring noble gas, radon is unique among its group for being radioactive. All of its isotopes are radioactive, with radon-222 being the most stable isotope, having a half-life of 3.8 days. Radon shares the characteristic chemical inertness of noble gases but poses significant health risks due to its radioactivity and ability to decay into radioactive daughter products.

Natural Occurrence

Radon is produced naturally from the radioactive decay of uranium and thorium, which are found in varying amounts in the Earth’s crust. It can accumulate in buildings, especially in confined areas such as basements and crawl spaces, from where it can seep out of rocks and soil. The concentration of radon gas in the environment can vary significantly depending on the geological composition of the area.


Due to its radioactive properties and health risks, the uses of radon are limited and highly specialized:

  • Radiation Therapy: Radon has been used in the past for radiation therapy to treat cancer, utilizing its radioactive decay to damage cancerous cells. However, its use has declined in favor of other radioisotopes with more favorable properties.
  • Scientific Research: Radon is used in some areas of scientific research, including studies of atmospheric phenomena, groundwater flow, and geology, to trace movements and investigate processes.

The discovery of radon expanded the understanding of noble gases and radioactive decay chains. Despite its limited practical applications, radon’s significance lies in its impact on health and safety, highlighting the importance of monitoring and mitigating radon exposure in homes and buildings to reduce the risk of lung cancer associated with radon inhalation.


Astatine (At)

Francium (Fr)