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88 franciumradiumactinium


Name, Symbol, Number radium, Ra, 88
Chemical series alkaline earth metals
Group, Period, Block 2, 7, s
Appearance silvery white metallic
Atomic mass (226) g/mol
Electron configuration [Rn] 7s2
Electrons per shell 2, 8, 18, 32, 18, 8, 2
Physical properties
Phase solid
Density (near r.t.) 5.5 g/cm³
Melting point 973 K
(700 °C, 1292 °F)
Boiling point 2010 K
(1737 °C, 3159 °F)
Heat of fusion 8.5 kJ/mol
Heat of vaporization 113 kJ/mol
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 819 906 1037 1209 1446 1799
Atomic properties
Crystal structure cubic body centered
Oxidation states 2
(strongly basic oxide)
Electronegativity 0.9 (Pauling scale)
Ionization energies 1st: 509.3 kJ/mol
2nd: 979.0 kJ/mol
Atomic radius 215 pm
Magnetic ordering nonmagnetic
Electrical resistivity (20 °C) 1 µΩ·m
Thermal conductivity (300 K) 18.6 W/(m·K)
CAS registry number 7440-14-4
Notable isotopes
Main article: Isotopes of radium
iso NA half-life DM DE (MeV) DP
226Ra trace 1602 y alpha 4.871 222Rn
228Ra syn 6.7 y beta- 0.046 228Ac

Radium is a chemical element, which has the symbol Ra and atomic number 88 (see the periodic table).

Its appearance is almost pure white, but it readily oxidizes on exposure to air, turning black. Radium is an alkaline earth metal that is found in trace amounts in uranium ores. It is extremely radioactive. Its most stable isotope, Ra-226, has a half-life of 1602 years and decays into radon gas.


Notable characteristics

The heaviest of the alkaline earth metals, radium is intensely radioactive and resembles Barium chemically. This metal is found (combined) in minute quantities in the uranium ore pitchblende, and various other uranium minerals. Radium preparations are remarkable for maintaining themselves at a higher temperature than their surroundings, and for their radiations, which are of three kinds: alpha rays, beta rays, and gamma rays. Radium also produces neutrons when mixed with beryllium.

When freshly prepared, pure radium metal is brilliant white, but blackens when exposed to air (probably due to nitride formation). Radium is luminescent (giving a faint blue color), corrodes in water to form radium hydroxide and is a bit more volatile than barium.


Some of the practical uses of radium are derived from its radiative properties. More recently discovered radioisotopes, such as cobalt-60 and caesium-137, are replacing radium in even these limited uses because several of these are much more powerful and others are safer to handle.

  • Formerly used in self-luminous paints for watches, clocks and instrument dials. More than 100 former watch dial painters who used their lips to shape the paintbrush died from the radiation. Soon afterward, the adverse effects of radioactivity were popularized. Radium was still used in dials as late as the 1950's. Objects painted with this paint may still be dangerous, and must be handled properly. Currently, tritium is used instead of radium. Although tritium still carries some risks, it is considered by many to be safer than radium.
  • When mixed with Beryllium it is a Neutron source for physics experiments.
  • Radium (usually in the form of radium chloride) is used in medicine to produce radon gas which in turn is used as a cancer treatment.
  • One unit for radioactivity, the non-SI curie, is based on the radioactivity of radium-226 (see Radioactivity).


Radium (Latin radius, ray) was discovered by Marie Curie and her husband Pierre in 1898 in pitchblende/uraninite from North Bohemia. While studying pitchblende the Curies removed uranium from it and found that the remaining material was still radioactive. They then separated out a radioactive mixture mostly consisting of barium which gave a brilliant red flame color and spectral lines which had never been documented before. In 1902 radium was isolated into its pure metal by Curie and Andre Debierne through the electrolysis of a pure radium chloride solution by using a mercury cathode and distilling in an atmosphere of hydrogen gas.

Historically the decay products of radium were known as Radium A, B, C, etc. These are now known to be isotopes of other elements as follows:

Radium emanation - radon-222
Radium A - polonium-218
Radium B - lead-214
Radium C - bismuth-214
Radium C1 - polonium-214
Radium C2 - thallium-210
Radium D - lead-210
Radium E - bismuth-210
Radium F - polonium 210

On February 4, 1936 radium E became the first radioactive element to be made synthetically.

During the 1930s it was found that worker exposure to radium by handling luminescent paints caused serious health effects which included sores, anemia and bone cancer. This use of radium was stopped soon afterward. This is because radium is treated as calcium by the body, and deposited in the bones, where radioactivity degrades marrow, and can mutate bone cells. Handling of radium has since been blamed for Marie Curie's premature death.


Radium is a decay product of uranium and is therefore found in all uranium-bearing ores. Radium was originally acquired from pitchblende ore from Joachimsthal, Bohemia (7 metric tons of pitchblende yields 1 gram of radium). Carnotite sands in Colorado provide some of the element, but richer ores are found in the Democratic Republic of the Congo, the Great Lakes area of Canada and can also be extracted from uranium processing waste. Large uranium deposits are located in Ontario, New Mexico, Utah, Australia, and in other places.


Its compounds color flames crimson carmine (rich red or crimson color with a shade of purple) and give a characteristic spectrum. Due to its geologically short half life and intense radioactivity, radium compounds are quite rare, occurring almost exclusively in uranium ores.

Fluorides: radium (II) fluoride (RaF2), Chlorides: radium (II) chloride (RaCl2), Bromides: radium (II) bromide (RaBr2), Iodides: radium (II) iodide (RaI2), Hydrides: no data, Oxides: radium (II) oxide (RaO), Sulfides: no data, Selenides: no data, Tellurides: no data, Nitrides: no data


Radium has 25 different isotopes, four of which are found in nature, with radium-226 being the most common. Ra-223, Ra-224, Ra-226 and Ra-228 are all generated in the decay of either U or Th. Ra-226 is a product of U-238 decay, and is the longest-lived isotope of radium with a half-life of 1602 years; next longest is Ra-228, a product of Th-232 breakdown, with a half-life of 6.7 years.


Radium is over one million times more radioactive than the same mass of uranium. Its decay occurs in at least seven stages; the successive main products have been studied and were called radium emanation or exradio (this is radon), radium A (polonium), radium B (lead), radium C (bismuth), etc. (The radon is a heavy gas, the later products are solids.) These products are themselves radioactive elements, each with an atomic weight a little lower than its predecessor.

Radium loses about 1% of its activity in 25 years, being transformed into elements of lower atomic weight with lead being a final product of disintegration.

The SI unit of radioactivity is the becquerel (Bq), equal to one disintegration per second. The curie is a non-SI unit defined as that amount of radioactivity which has the same disintegration rate as 1 gram of Ra-226 (3.7 x 1010 disintegrations per second, or 37 GBq).


Radium is highly radioactive and its decay product, radon gas is also radioactive. Since radium is chemically similar to calcium, it has the potential to cause great harm by replacing it in bone. Inhalation, injection, ingestion or body exposure to radium can cause cancer and other body disorders. Stored radium should be ventilated to prevent accumulation of radon.

Emitted energy from the decay of radium ionizes gases, affects photographic plates, causes sores on the skin, and produces many other detrimental effects.

Further reading

  • Scientific American (Macklis RM, The great radium scandal. Sci.Am. 1993 Aug: 269(2):94-99)
  • Clark, Claudia. (1987). Radium Girls: Women and Industrial Health Reform, 1910-1935. University of North Carolina Press. ISBN 0807846406.
  • Ken Silverstein, Harper's Magazine, November 1998; The radioactive boy scout: when a teenager attempts to build a breeder reactor - case of David Hahn who managed to secure materials and equipment from businesses and information from government officials to develop an atomic energy radiation project for his Boy Scout merit-badge.


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