Radium
For glow in the dark paint.
Atomic Number: 88
Atomic Symbol: Ra
Atomic Weight: 226.0254
Electron
Configuration: [Rn]7s2
History
(L. radius, ray) Radium was discovered in 1898 by Mme. Curie in the
pitchblende or uraninite of North
Bohemia, where it occurs. There is
about 1 g of radium in 7 tons of pitchblende. The element was
isolated in
1911 by Mme. Curie and Debierne by; the electrolysis of a solution of pure
radium chloride,
employing a mercury cathode; on distillation in an
atmosphere of hydrogen this amalgam yielded the
pure metal.
Sources
Originally, radium was obtained from the rich pitchblende ore found in
Joachimsthal, Bohemia. The
carnotite sands of Colorado furnish some radium, but richer ores are found in
the Republic of Zaire and
the Great Lake region of Canada. Radium is present in all uranium minerals,
and could be extracted, if
desired, from the extensive wastes of uranium processing. Large uranium
deposits are located in Ontario,
New Mexico, Utah, Australia, and elsewhere.
Properties
Radium is obtained commercially as bromide and chloride; it is doubtful if any
appreciable stock of the
isolated element now exists.
The pure metal is brilliant white when freshly prepared, but blackens on
exposure to air, probably due to formation of the nitride.
It exhibits luminescence, as do its slats; it
decomposes in water and is somewhat more volatile than barium.
It is a member of the alkaline-earth
group of metals. Radium imparts a carmine red color to a flame.
Radium emits alpha, beta, and gamma
rays and when mixed with beryllium produce neutrons. One gram of 226Ra
undergoes 3.7 x 10¹⁰
disintegrations per s.
The curie is defined as that amount of radioactivity which has the same
disintegration rate as 1 g of 226Ra.
Twenty five isotopes are now known; radium 226, the common
isotope, has a half-life of 1600 years.