Promethium was discovered in 1945. It was the last rare earth lanthanide element to be discovered. It is very radioactive element but unstable. It is used in luminous paint and atomic batteries.
History and Discovery
In 1902 Bohuslav Brauner predicted the existence of an element in between neodymium (60) and samarium (62). The first claim was published by Luigi Rolla and Lorenzo Fernandes who separated mixture of few rare earth element nitrate concentrate from monazite by fractional crystallization, they named that element ‘’florentium’’ . Smith Hopkins and Len Yntema in 1926 published the discovery and named it ‘’illinium’’. Both discoveries were not identical to didymium but have impurities (barium, chromium and platinum). In 1934, Josef Mattauch proposed that element 61 was unable to form stable isotopes. In 1945 Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell, successfully isolated promethium through the separation and analysis of fission product of uranium fuel that was irradiated in a graphite reactor. The name ‘’prometheum’’ was given by Grace Mary Coryell, and it has been derived from Prometheus, the Titan in Greek mythology who stole fire from Mount Olympus and brought it down to the humans . It has also been produced by slow neutron bombardment of the isotope neodymium-146, and the resultant isotope neodymium-147 decay into promethium-147 through beta decay and have a half- life of 11 days .
|Periodic Table Classification||Group n/a
|State at 20C||Solid|
|Electron Configuration||[Xe] 4f5 6s2|
|Electron Shell||2, 8, 18, 23, 8, 2|
|Density||7.30 g.cm-3 at 20°C|
|Atomic Mass||145.00 g.mol -1|
|Electronegativity according to Pauling||1.13|
Promethium is an extremely rare element and only 500-600g of promethium is naturally present in the earth’s crust. Promethium is not found in free or elemental form in nature. It is found in uranium ores. It can be produced as a by -product of uranium fission reaction. Uranium is responsible for 560g of promethium in the Earth crust. It has been detected in the stars, present in the spectrum of the star HR 465 (Andromeda: 48 constellations) and HD 101065 (Przbylski’s star: rapidly oscillating Ap star). Due to short half-life of its isotopes they are formed near the surface of those star.
Promethium is radioactive element; metallic promethium is silvery white in color and its salts glow in the dark to produce pale blue or green light. Promethium chemical symbol is Pm with atomic number 61 and atomic weight is 145. Its melting point is 1042OC, which is higher than neodymium and lower than samarium. Similarly, boiling point is 3000OC is greater than samarium and less than neodymium. Promethium density at room temperature is 7.26 g/cm3.
Promethium is unstable due to which its chemical properties are not fully known. It belongs to the cerium group of lanthanide. Promethium forms stable compounds in +3 oxidation state. Pm3+ ions are formed in acidic solution and when treated with ammonia it forms gelatinous light- brown sediments of hydroxide, which are insoluble in water. When dissolved in hydrochloric acid it produces water soluble yellow salt PmCl3. Similarly, when dissolved in nitric acid it forms nitrate solution Pm (NO3)3. Oxidizing or reducing agent show that its ions are not easily oxidized or reduced.
Significance and Uses
- Promethium-147 are used in luminous paint, atomic batteries in which they are converted into electric current by using promethium source between two semiconductors.
- It is mostly used for research purpose in laboratories.
- Promethium-147 does not cause aging of the phosphor therefore used in signal lights that absorbs beta radiation emitted by promethium-147 and emits lights.
- It is also used for nuclear safety reasons.
- It is used to measure the thickness of materials.
- It is also used as portable X-ray in radioisotope thermoelectric generators to provide electricity for space.
- It is widely used to make lasers to communicate with submerged submarines.
- It can be used as a beta radiation source.
Promethium is slightly dangerous due its radioactivity. The most affected human organ is the bone tissues. It has no important biological role in the humans, plants or animals.
Isotopes of Promethium
Promethium has no stable isotopes. Promethium-145 is the most stable isotope which has a half- life of 17.7 years. It has eighteen nuclear isomers having mass number 133 to 142, 144, 148, 149, 152 and 154. The most stable of them is promethium-148m with a half- life of 43.1 days .
. Rolla, L.; Fernandes, L. (1927). “Florentium or Illinium?”. Nature. 119(3000): 637.
. Emsley 2011, p. 428.
. Gagnon, Steve. “The Element Promethium”. Jefferson Lab. Science Education. Retrieved 26 February2012.