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|Name, symbol||Promethium, Pm|
|Appearance||Metallic, silvery, glowing|
|Promethium in the periodic table|
|Standard atomic weight (Ar)|
|Group, block||n/a; f-block|
|Electron configuration||[Xe] 4f5 6s2|
|2, 8, 18, 23, 8, 2|
|Melting point||1315 K (1042 °C, 1908 °F)|
|Boiling point||3273 K (3000 °C, 5432 °F)|
|Density near r.t.||7.26 g/cm3|
|Heat of fusion||7.13 kJ/mol|
|Heat of||289 kJ/mol|
|Oxidation states||+2, +3|
1st: 540 kJ/mol |
2nd: 1050 kJ/mol
3rd: 2150 kJ/mol
|Atomic radius||empirical: 183 pm|
|Covalent radius||199 pm|
|Thermal expansion||9.0 µm/(m·K) (at room temperature)|
|Thermal conductivity||17.9 W/(m·K)|
|Electrical resistivity||0.75 Ω·m (at 20 °C) (estimated)|
|Young's modulus||α form: est. 46 GPa|
|Shear modulus||α form: est. 18 GPa|
|Bulk modulus||α form: est. 33 GPa|
|Poisson ratio||α form: est. 0.28 GPa|
|CAS Registry Number||7440-12-2|
|Discovery||Chien Shiung Wu, Emilio Segrè, Hans Bethe (1942)|
|First isolation||Charles D. Coryell, Jacob A. Marinsky, Lawrence E. Glendenin (1945)|
|Named by||Grace Mary Coryell (1945)|
Promethium (Pm) is an extremely radioactive lanthanide. It is one of two classical elements lighter than bismuth, with no stable isotopes, the other being technetium. It is not encountered in nature except for traces and is primarily synthesized in labs.
The chemistry of promethium is very similar to that of other lanthanides.
Promethium is a silvery-gray metal, which glows in dark. It readily oxidizes in air.
The most stable isotope of the element is promethium-145, which has a specific activity of 940 Ci/g (35 TBq/g) and a half-life of 17.7 years via electron capture.
Promethium is extremely hard to find, but some sellers do exist. It's very expensive.
While it's possible to reduce promethium from the fluorescent dye it's commonly available, one would need a very large amount of Pm dye, large enough that its radioactivity becomes a serious hazard. As such, it's not a good idea to isolate this metal, unless one has the setting to do this safely.
In industry, promethium is synthesized by bombarding uranium-235 (enriched uranium) with thermal neutrons to produce promethium-147 as a fission product. Pm-145, the more stable isotope, can be produced via the radioactive decay of samarium-145.
- Element collection
- Study radioactivity
- Luminous paint
- Atomic batteries
Promethium is highly radioactive and proper protection should be worn when handling the compound.
In closed vials, kept in lead-lined boxes.