2007 Schools Wikipedia Selection. Related subjects: Chemical elements

61 neodymiumpromethiumsamarium


Periodic Table - Extended Periodic Table
Name, Symbol, Number promethium, Pm, 61
Chemical series lanthanides
Group, Period, Block n/a, 6, f
Appearance metallic
Atomic mass [145] (0) g/mol
Electron configuration [Xe] 4f5 6s2
Electrons per shell 2, 8, 18, 23, 8, 2
Physical properties
Phase solid
Density (near r.t.) 7.26 g·cm−3
Melting point 1315  K
(1042 ° C, 1908 ° F)
Boiling point 3273 K
(3000 ° C, 5432 ° F)
Heat of fusion 7.13 kJ·mol−1
Heat of vaporization 289 kJ·mol−1
Atomic properties
Crystal structure hexagonal
Oxidation states 3
(mildly basic oxide)
Electronegativity  ? 1.13 (Pauling scale)
Ionization energies
( more)
1st: 540 kJ·mol−1
2nd: 1050 kJ·mol−1
3rd: 2150 kJ·mol−1
Atomic radius 185 pm
Atomic radius (calc.) 205 pm
Magnetic ordering no data
Electrical resistivity ( r.t.) est. 0.75 µΩ·m
Thermal conductivity (300 K) 17.9 W·m−1·K−1
Thermal expansion ( r.t.) (α, poly)
est. 11 µm/(m·K)
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
CAS registry number 7440-12-2
Selected isotopes
Main article: Isotopes of promethium
iso NA half-life DM DE ( MeV) DP
145Pm syn 17.7 y ε 0.163 145Nd
146Pm syn 5.53 y ε 1.472 146Nd
β- 1.542 146Sm
147Pm syn 2.6234 y β- 0.224 147Sm

Promethium ( IPA: /prə(ʊ)ˈmiːθiəm/) is a chemical element in the periodic table that has the symbol Pm and atomic number 61.

Notable characteristics

Promethium has one semi-stable isotope (145), it is a soft beta emitter; it does not emit gamma rays, but beta particles impinging on elements of high atomic numbers can generate X-rays. Pure promethium exists in two allotropic forms, and its chemistry is similar to other lanthanides. Promethium salts luminesce in the dark with a pale blue or greenish glow due to their high radioactivity. Promethium can be found in traces in some uranium ores as a fission product.


Uses for promethium include:

  • Beta radiation source for thickness gauges.
  • Light source for signals that require reliable, independent operation (using phosphor to absorb the beta radiation and produce light).
  • In a nuclear battery in which photocells convert the light into electric current, yielding a useful life of about five years using 147-Pm.
  • Possibly in the future as a portable X-ray source, as an auxiliary heat or power source for space probes and satellites.


The existence of promethium was first predicted by Bohuslav Brauner in 1902; this prediction was supported by Henry Moseley in 1914, who found a gap for a missing element which would have atomic number 61, but was unknown (however, Moseley of course had no sample of the element to verify this). Several groups claimed to have produced the element, but they could not confirm their discoveries because of the difficulty of separating promethium from other elements. Proof of the existence of promethium was obtained in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell during the analysis of byproducts of uranium fission; however, being too busy with defense-related research during World War II, they did not announce their discovery until 1947. The name promethium is derived from Prometheus in Greek mythology, who stole the fire of the sky and gave it to mankind. The name was suggested by Grace Mary Coryell, Charles Coryell's wife, who felt that they were stealing fire from the gods.

In 1963, ion-exchange methods were used to prepare about 10 grams of promethium from atomic reactor fuel processing wastes.

Today, promethium is still recovered from the byproducts of uranium fission; it can also be produced by bombarding 146Nd with neutrons, turning it into 147Nd which decays into 147Pm through beta decay with a half-life of 11 days.


Promethium can be formed as a product of uranium fission. Only trace amounts can be found in naturally occurring ores: a sample of pitchblende has been found to contain promethium at a concentration of four parts per quintillion (1018) by mass.

Promethium has also been identified in the spectrum of the star HR 465 in Andromeda, and possibly HD 101065 ( Przybylski's star) and HD 965.


Promethium compounds include:

  • Chlorides
    • PmCl3
  • Bromides
    • PmBr3
  • Oxides
    • Pm2O3


36 radioisotopes of promethium have been characterized, with the most stable being 145Pm with a half-life of 17.7 years, 146Pm with a half-life of 5.53 years, and 147Pm with a half-life of 2.6234 years. All of the remaining radioactive isotopes have half-lives that are less than 364 days, and the majority of these have half lives that are less than 27 seconds. This element also has 11 meta states with the most stable being 148Pmm (T½ 41.29 days), 152Pmm2 (T½ 13.8 minutes) and 152Pmm (T½ 7.52 minutes).

The isotopes of promethium range in atomic weight from 127.9482600 u (128Pm) to 162.9535200 u (163Pm). The primary decay mode before the longest-lived isotope, 145Pm, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 145Pm are neodymium (Nd) isotopes and the primary products after are samarium (Sm) isotopes.


Promethium must be handled with great care because of its high radioactivity. In particular, promethium can emit X-rays during its beta decay. Note that its half-life is less than that of plutonium-239 by a factor of multiple thousands to tens of thousands. Promethium has no biological role.

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