Radon is radioactive gas and was discovered by 1899 by Ernest Rutherford and Robert B. Owens. It is formed by the radioactive decay of radium. Radon is the heaviest gas and a known air pollutant.

History and Discovery

Radon was discovered by Ernest Rutherford and Robert B. Owens in 1899.  In the same year Pierre and Marie Curie observed gas emission from radon. And Friedrich Ernst Dom (1900) named the radioactive gas ‘Radium Emanation’ [1]. Ramsay and Robert Whytlaw-Gray found various characteristics of this distinct gas, including density and melting temperature in 1909. They proposed that radon is the heaviest among all known gases.  In early time, Radon was named as niton that was derived from Latin word ‘’nitens’’ meaning “shinning”. The International Union of Pure and Applied Chemistry (IUPAC) named it as Radon in 1923 [2].


Periodic Table ClassificationGroup 18
Period 6
State at 20CGas
ColorColorless gas
Electron Configuration[Xe] 4f14 5d10 6s2 6p6
Electron Number86
Proton Number86
Electron Shell2, 8, 18, 32, 18, 8
Density9.73 g.cm-3 at 20°C
Atomic number86
Atomic Mass222.00 g.mol -1
Electronegativity according to Pauling2.20


Radon is present in indoor and outdoor areas. It is produced by radioactive decay of radium and thorium. Naturally, radium is present in uranium ores. Uranium is present in small quantity in all soil and rocks. Radon quantity in atmosphere is very low but in houses its concentration is very high. Radon gas can enter in the building through cracks in floor and wall. Its concentration is very high in mining areas, spring waters and hot water. Japan and Germany have radium rich springs that emit high concentrations of radon. Ground water has high concentration of radon due to continuous radioactive decay of radon as compared to the surface water. It is also found in petroleum as radon and propane has the same temperature and pressure curves and is often isolated during the purification of petroleum [3].

Physical Characteristics

Radon is a colorless, odorless and tasteless gas which makes it presence hard to detect by humans. Radon seeps up through the ground and diffuses into air. Radon exhibits brilliant yellow phosphorescence at temperature below its freezing point. The density of radon is significantly high and is nine times higher than air (9.73kg/m3). Radon is about 100 times heavier than hydrogen. Unlike oxygen, radon is a single atom gas which makes it easily penetrate able through various obstacles, including paper, plastic bags, paints, building materials like gypsum board, concrete block and certain insulations. Radon gas liquefies at -61.80C and freezes at-710C.  Radon is springily soluble in water but more soluble in organic solvents. The atomic number of radon is 86 and atomic mass is 222.

Chemical Characteristics

Radon is inert gas and chemically unreactive. Radon is inert to most common chemical reactions including combustion. It is metalloid which means radon lies on the diagonal of the periodic table between the true metals and nonmetals, so it exhibits characteristics of both. In its ionic state it can displace H+, Na+, Cs+, Ca+ and Ba2+ ions. Radon has lower electronegativity than xenon, so it is relatively reactive. The stability of radon hydrate is similar with the hydrates of chlorine or sulfur dioxide but significantly higher than hydrates of hydrogen sulfide. Radon is oxidized by strong oxidizing agent like fluorine and forms radon difluoride.  It is mostly exit in two possible states 0 and +2.

Significance and Uses

  • Radon is commercially for radiation therapy. The radioactivity of radon is molecular damaging is being widely used to kill cancerous cell.
  • In groundwater, the changing concentration of radon is helpful for examination of earthquake prediction.
  • Radon has been used for presumed medical effects in spas.
  • It is useful in geological research for tracking air masses.
  • Radon is needed and delivered in sealed gold needles.
  • It is also used in hydrologic research due to its rapid loss of air.
  • Radon is helpful in exploration of new reserve of petroleum and uranium.

Health Hazards

The primary routes of human exposure to radon is inhalation and ingestion. High concentration of radon in underground water may contribute to radon toxicity [4]. Building materials like granite countertops in a home would increase radiation level. Radon quickly decay and produced radioactive particles which when inhaled damage lungs cells and lead to lung cancer. Leukemia is also caused by radon exposure in adults and children. Radon exposure level is higher for people who are working in uranium processing factories and dealing with phosphate fertilizers. Radon is second leading cause of lung cancer after cigarette smoking.

Isotopes of Radon

Radon has thirty-seven isotopes having atomic masses ranging from 193 to 229. It has no stable isotopes. 222Rn is the stable isotope having a half-life of 3.8 days. It is decay product of 226Rn and 238U. Three isotopes of radon have a half –life of over an hour like 211Rn, 210Rn and 224Rn. 220Rn isotope is product of natural decay of stable thorium.


[1]. Dorn, F. E. (1900). “Die von radioactiven Substanzen ausgesandte Emanation“(PDF). Abhandlungen der Naturforschenden Gesellschaft zu Halle23: 1–15


[3].“Potential for Elevated Radiation Levels In Propane”(PDF). National Energy Board. April 1994. Retrieved 2009-07-07.

[4]. https://www.cancer.org/cancer/cancer-causes/radiation-exposure/radon.html