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Radon Facts

Radon Chemical and Physical Properties


This is not radon, but radon looks like this.\

This is not radon, but radon looks like this. Radon glows red in a gas discharge tube, though it is not used in tubes because of its radioactivity. This is xenon in a gas discharge tube, with the colors changed to show what radon would look like.

Jurii, Creative Commons License This diagram of a radon atom shows the electron shell.

This diagram of a radon atom shows the electron shell.

Greg Robson,Creative Commonns License This is a periodic table tile for the element radon.

This is a periodic table tile for the element radon.

Todd Helmenstine


Atomic Number: 86

Symbol: Rn

Atomic Weight: 222.0176

Discovery: Fredrich Ernst Dorn 1898 or 1900 (Germany), discovered the element and called it radium emanation. Ramsay and Gray isolated the element in 1908 and named it niton.

Electron Configuration: [Xe] 4f14 5d10 6s2 6p6

Word Origin: from radium. Radon was once called niton, from the Latin word nitens, which means 'shining'

Isotopes: At least 34 isotopes of radon are known ranging from Rn-195 to Rn-228. There are no stable isotopes of radon. The isotope radon-222 is the most stable isotope and called thoron and emanates naturally from thorium. Thoron is an alpha-emitter with a half-life of 3.8232 days. Radon-219 is called actinon and emanates from actinium. It is an alpha-emitter with a half-life of 3.96 sec.

Properties: Radon has a melting point of -71°C, boiling point of -61.8 °C, gas density of 9.73 g/l, specific gravity of the liquid state of 4.4 at -62°C, specific gravity of the solid state of 4, usually with a valence of 0 (it does form some compounds, however, such as radon fluoride). Radon is a colorless gas at normal temperatures. It is also the heaviest of the gases. When it is cooled below its freezing point it displays a brilliant phosphorescence. The phosphorescence is yellow as the temperature is lowered, becoming orange-red at the temperature of liquid air. Inhalation of radon presents a health risk. Radon build-up is a health consideration when working with radium, thorium, or actinium. It is also a potential issue in uranium mines.

Sources: It is estimated that each square mile of soil to a depth of 6 inches contains approximately 1 g of radium, which releases radon to the atmosphere. The average concentration of radon is about 1 sextillion parts of air. Radon naturally occurs in some spring waters.

Element Classification: Inert Gas

Density (g/cc): 4.4 (@ -62°C)

Melting Point (K): 202

Boiling Point (K): 211.4

Appearance: heavy radioactive gas

Specific Heat (@20°C J/g mol): 0.094

Evaporation Heat (kJ/mol): 18.1

First Ionizing Energy (kJ/mol): 1036.5

Lattice Structure: Face-Centered Cubic

CAS Registry Number: 10043-92-2

Radon Trivia:

  • Ernest Rutherford is sometimes credited with the discovery of radon. He actually discovered the alpha particle radiation given off by radon.
  • Radon became the official name for element 86 in 1923. The IUPAC chose radon from the names radon (Rn), thoron (Tn) and actinon (An). The other two names are given to isotopes of radon. Thoron is Rn-220 and actinon became Rn-219.
  • Other suggested names for radon included radium emanation, niton, extadio, exthorio, exactinio, akton, radeon, thoreon and actineon.
  • The U.S. Environmental Protection Agency lists radon as the second highest cause of lung cancer.

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.) International Atomic Energy Agency ENSDF database (Oct 2010)

Quiz: Ready to test your radon facts knowledge? Take the Radon Facts Quiz.

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