Periodic Table


Atomic number: 61
Atomic weight: 145
Symbol: Pm
Group number: (lanthanide)
Electronic configuration: [Xe].4f5.6s2


Great care is required while handling promethium as a consequence of its radioactivity. Promethium salts luminesce in the dark with a pale blue or greenish glow, due to their high radioactivity. Ion-exchange methods led to the preparation of about 10 g of promethium from atomic reactor fuel processing wastes in early 1963.

Little is yet generally known about the properties of metallic promethium. More than 30 promethium compounds have been prepared. Promethium is a rare earth metal. It appears that there is no known Pm existing in the earth's crust.

General information

Discoveror: J. A. Marinsky, Lawrence Glendenin, Charles D. Coryell
Date discovered: 1945
Discovered at: United States
Meaning of name: Named after "Prometheus" in Greek mythology, who stole fire from the gods

Physical data

Standard state: solid at 298 K
Colour: metallic
Density of solid at ambient temperature/kg m-3: 7264
Molar volume/cm3: 20.23

Radii /pm

Atomic: 205
Covalent (single bond):
Pauling radius for the ion [Pm]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius219.0no datano data33.3


Both values are quoted on the Pauling scale.

Pauling: no data
Allred Rochow: 1.07

Crystal Structure


The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 1373
boiling point: 3273

Enthalpies /kJ mol-1

fusion: 7.13
vaporization: 289

single bond enthalpies:
Pm-F Pm-Cl Pm-Br Pm-I Pm-Pm
no data no data no data 305 no data

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/Pm.html