Radium Facts

Chemical & Physical Properties

Luminescent clock dial
A 1950s radium clock dial, previously exposed to UV-A light.

Arma95/Wikimedia Commons/CC BY-SA 3.0

Atomic Number: 88

Symbol: Ra

Atomic Weight: 226.0254

Electron Configuration: [Rn] 7s2

Word Origin: Latin radius: ray

Element Classification: alkaline earth metal


It was discovered by Pierre and Marie Curie in 1898 (France/Poland). It was isolated in 1911 by Mme. Curie and Debierne.


Sixteen isotopes of radium are known. The most common isotope is Ra-226, which has a half-life of 1620 years.


Radium is an alkaline earth metal. Radium has a melting point of 700°C, boiling point of 1140°C, specific gravity estimated to be 5, and valence of 2. Pure radium metal is bright white when freshly prepared, although it blackens upon exposure to air. The element decomposes in water. It is somewhat more volatile than the element barium. Radium and its salts exhibit luminescence and impart a carmine color to flame. Radium emits alpha, beta, and gamma rays. It produces neutrons when mixed with beryllium. A single gram of Ra-226 decays at the rate of 3.7x1010 disintegrations per second. [The curie (Ci) is defined to be the quantity of radioactivity which has the same rate of disintegration as 1 gram of Ra-226.] A gram of radium produces around 0.0001 ml (STP) of radon gas (emanation) per day and about 1000 calories per year. Radium loses about 1% of its activity over 25 years, with lead as its final disintegration product. Radium is a radiological hazard. Stored radium requires ventilation to prevent the build-up of radon gas.


Radium has been used to produce neutron sources, luminous paints, and medical radioisotopes.


Radium was discovered in pitchblende or uraninite. Radium is found in all uranium minerals. There is approximately 1 gram of radium for each 7 tons of pitchblende. Radium was first isolated by electrolysis of a radium chloride solution, using a mercury cathode. The resulting amalgam yielded pure radium metal upon distillation in hydrogen. Radium is commercially obtained as its chloride or bromide and tends not to be purified as an element.

Physical Data

Density (g/cc): (5.5)

Melting Point (K): 973

Boiling Point (K): 1413

Appearance: silvery white, radioactive element

Atomic Volume (cc/mol): 45.0

Ionic Radius: 143 (+2e)

Specific Heat (@20°C J/g mol): 0.120

Fusion Heat (kJ/mol): (9.6)

Evaporation Heat (kJ/mol): (113)

Pauling Negativity Number: 0.9

First Ionizing Energy (kJ/mol): 509.0

Oxidation States: 2


  • CRC Handbook of Chemistry & Physics, 18th Ed.
  • Crescent Chemical Company, 2001.
  • Lange's Handbook of Chemistry, 1952.
  • Los Alamos National Laboratory, 2001.
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Your Citation
Helmenstine, Anne Marie, Ph.D. "Radium Facts." ThoughtCo, Apr. 5, 2023, thoughtco.com/radium-facts-606583. Helmenstine, Anne Marie, Ph.D. (2023, April 5). Radium Facts. Retrieved from https://www.thoughtco.com/radium-facts-606583 Helmenstine, Anne Marie, Ph.D. "Radium Facts." ThoughtCo. https://www.thoughtco.com/radium-facts-606583 (accessed May 29, 2023).