Radon is the last member of group 18. Its name is derived from radium from which it is originates. It has an atomic mass of 222.0176 and an atomic radius of 1.34 Angstrom.
It was discovered in 1900 by the German chemist Fredrich Ernst Dorn. Radon has an extremely short half-life of 3.8 days, which explains why so little research has been done on it. However, chemists have been able to make compounds of radon.
Radon is found naturally in rock and soil. However, it is a serious health hazard if found in high concentrations. Amazingly, millions of homes and buildings through out the world contain high levels of radon gas. To combat the risk of exposure to large quantities of the gas, the United States government has developed a program that identifies areas of the country with particularly high levels of the radioactive gas.
Radon is a monatomic gas, which has no colour, taste, or odour. It has a melting point of 202K and a boiling point of 211K. It has a cubic-faced crystal structure.
Radon, unlike other noble gases, cannot be obtained from fractional distillation of air. This is because it is found in such small quantities that extraction from the atmosphere is not economical. It is therefore obtained by passing air through a solution of radium salt and collecting the air and radon gas present in the solution.
Radon is mainly used in medicine where it is employed to treat many forms of cancer. Treatment involves placing a radon seed (radon gas contained within a glass tube) into the tumour of a cancer sufferer.