Radon is a heavy, colorless, odorless, radioactive noble gas produced by the decay of uranium and thorium in rocks and soil. It is the densest gas at standard conditions and a significant inhalation hazard linked to lung cancer.
Radon is a naturally occurring radioactive noble gas produced by the decay of uranium (U) and thorium (Th) present in the Earth’s crust. It is part of the uranium-238 decay chain:
\(\mathrm{^{238}U \rightarrow ^{226}Ra \rightarrow ^{222}Rn + \alpha}\)
The isotope radon-222 is the most stable and common form, with a half-life of 3.8 days.
Radon is dangerous because it emits alpha radiation during radioactive decay. When inhaled, it can damage lung tissue, increasing the risk of lung cancer. Prolonged exposure to high levels of radon gas, especially indoors, is a leading cause of lung cancer after smoking.
Radon has several isotopes, all radioactive. The most important ones are:
Among them, Rn-222 is the most significant in environmental and health contexts.
Radon gas is found everywhere in small amounts. It seeps naturally from soil, rocks, and groundwater. It tends to accumulate in enclosed spaces such as basements and underground buildings where ventilation is poor.
Radon is a colorless, odorless, and tasteless gas at room temperature. It condenses into a colorless liquid below −61.8 °C and freezes into a yellow solid below −71 °C. It is the densest noble gas and slightly soluble in water and organic solvents.
As a noble gas, radon is chemically inert under most conditions. However, under extreme conditions, it can form compounds such as radon difluoride (RnF2) and possibly oxides of radon. These compounds are unstable and only observed in laboratory conditions.
\(\mathrm{Rn + F_2 \rightarrow RnF_2}\)
Radon is a major source of natural background radiation. When radon gas decays, it produces radioactive radon daughters (like polonium-218 and lead-214) that attach to dust particles. Inhalation of these particles leads to alpha radiation exposure inside the lungs.
Radon exposure can be reduced by:
Radon has limited but specialized applications:
Radon is part of the noble gases (Group 18) because it has a complete outer electron shell (6s26p6), making it chemically inert under normal conditions, similar to helium, neon, and argon.
Long-term exposure to radon and its decay products is the second leading cause of lung cancer after smoking. According to the World Health Organization (WHO), safe indoor radon levels should be below 100 Bq/m³ to minimize risk.