- Radon (Rn) is a colorless, odorless, and tasteless noble gas with atomic number 86, belonging to Group 18 of the periodic table, alongside helium, neon, argon, krypton, and xenon.
- Its electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶, giving it a complete octet of valence electrons, which makes it chemically inert under normal conditions. A radon atom contains eighty-six protons, eighty-six electrons, and a variable number of neutrons depending on the isotope.
- The most stable isotope is radon-222 (²²²Rn), which has a half-life of about 3.8 days and is a decay product of radium-226 (²²⁶Ra).
- Radon was discovered in 1900 by German chemist Friedrich Ernst Dorn, who observed it as a radioactive gas emitted by radium. Initially referred to as “radium emanation,” it was later renamed radon in 1923. The discovery contributed significantly to the study of radioactivity, furthering the work of Marie Curie and other pioneers in nuclear science.
- Physically, radon is the heaviest known noble gas, with a density about 9.7 times greater than air. At standard temperature and pressure, it exists as an invisible gas, but when cooled below its freezing point (−71 °C or −96 °F), it condenses into a colorless liquid and eventually forms a glowing yellowish solid at even lower temperatures. Despite being chemically inert, radon can form clathrates (gas trapped in crystal lattices) with water or certain organic compounds under special conditions.
- Chemically, radon is largely unreactive, consistent with the noble gases. However, under extreme conditions, it can form compounds such as radon difluoride (RnF₂), demonstrating weak chemical activity. Its reactivity is far lower than that of lighter noble gases like xenon.
- Applications of radon are limited due to its radioactivity and health risks. Historically, it was used in cancer radiotherapy because of its strong alpha radiation, being sealed in small tubes and implanted in tumors. Today, its medical use has declined, replaced by safer and more controlled isotopes. Radon has also been employed in hydrology and geology as a natural tracer for groundwater movement and earthquake prediction, since its radioactive decay can reveal subsurface geological activity.
- Biologically, radon is extremely hazardous. When inhaled, radon gas and its radioactive decay products, such as polonium isotopes, lodge in the lungs, where they emit alpha radiation. This damages lung tissue and increases the risk of lung cancer. In fact, radon is the second leading cause of lung cancer after smoking. Smokers exposed to radon face an even higher risk due to the combined effects of tobacco and radiation.
- Environmentally, radon is a naturally occurring gas that seeps from soil and rock, especially in regions rich in uranium, thorium, and radium. It accumulates in enclosed spaces such as basements, mines, and poorly ventilated buildings, where it poses significant health risks. Radon testing and ventilation are common safety measures in many countries. Since its isotopes decay quickly, radon does not accumulate on a large global scale, but locally, it can be a serious hazard.
