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Promethium,  61Pm
General properties
Name, symbol Promethium, Pm
Pronunciation /proʊˈmiːθiəm/
Appearance Metallic, silvery, glowing
Promethium in the periodic table


Atomic number 61
Standard atomic weight (Ar)
Group, block n/a; f-block
Period period 6
Electron configuration [Xe] 4f5 6s2
per shell
2, 8, 18, 23, 8, 2
Physical properties
Phase Solid
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
Atomic properties
Oxidation states +2, +3
energies 1st: 540 kJ/mol
2nd: 1050 kJ/mol
3rd: 2150 kJ/mol
Atomic radius empirical: 183 pm
Covalent radius 199 pm
Crystal structure
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)
Magnetic ordering paramagnetic
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)
· references

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.


To do


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