Promethium
The only radioactive lanthanide, used in luminous paint.
Inside the Promethium atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Promethium atom step by step.
Electron configuration
[Xe] 4f5 6s2
A neutral Promethium atom has 61 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 1315 K (1042 °C)
- Boiling point
- 3273 K (3000 °C)
- Density
- 7.26 g/cm³
- Electronegativity
- 1.13 Pauling
- Atomic radius
- 185 pm
- 1st ionization energy
- 540 kJ/mol
- Category
- Lanthanides
Discovery & naming
- Discovered
- 1945
- Discovered by
- Marinsky, Glendenin, and Coryell
- Origin of name
- Prometheus of Greek mythology.
Notable uses
Luminous paint and nuclear-powered batteries.
Where Promethium comes from
Human synthesis
Has no stable isotope. Only vanishing natural traces survive, so usable promethium comes from reactors.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 61
- Atomic mass
- [145]
- Category
- Lanthanides
- Group · Period
- — · 6
- Block
- f-block
- Shells
- 2 · 8 · 18 · 23 · 8 · 2