Radium is the heaviest member of the alkaline earth group of elements (Group IIA) and is radioactive. Other members of the group are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).
The pure metal was isolated in 1911 by Madame Curie and Debierne by electrolysis of radium chloride using a mercury cathode. There is about 1 gram of Ra in each ton of pitchblende, an ore containing uranium. Pierre and Marie Curie discovered the element from this source in 1898.
Extensive deposits of radium-bearing ores - which also contain uranium - are found in Zaire and Canada.
The pure metal is brilliant white when freshly prepared, but it tarnishes in air, possibly through the formation of radium nitride on the metal's surface.
Radium and its salts luminesce, and, as with the other Group IIA elements, it reacts with water. It also gives a red color to flames, similar to calcium and strontium.
The element emits alpha, beta, and gamma radiation. The half-life for alpha emission by 226Ra is 1600 years. The unit of radioactivity, the curie (Ci), is defined as the amount of radioactivity that has the same disintegration as 1 gram of 226Ra.
Various 'radiums' labeled A, B, C, D, E, and F were discovered by Ernest Rutherford and Harriet Brooks in the solid deposit left on the insides of glass containers confin-ing radon gas. These are actually radio-active isotopes of Po, Pb and Bi.
One gram of radium produces about 4190 kJ of energy per year.
Radium is used in self-luminous paints and in medicine for the radiation treatment of some cancers.