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Periodic table / Lanthanoids

61Promethium

Promethium is a lanthanoid in period 6, in the lanthanoid series. At 25 °C it is a solid.

Pm
Shells: 2, 8, 18, 23, 8, 2. A simple picture: electrons do not move in circles.
Symbol
Pm
Atomic number
61 protons in the nucleus
Standard atomic weight
None. Promethium has no stable isotopes, so the mass of a sample depends on which isotopes it holds.
Electron configuration
[Xe] 4f5 6s2
Electrons in each shell
2, 8, 18, 23, 8, 2
Group, period, block
–, 6, f
Family
Lanthanoids
State at 25 °C
solid
Electronegativity
no value
First ionisation energy
538.6 kJ/mol (5.58187 eV)
Where these numbers come from

Atomic weight: IUPAC CIAAW, abridged standard atomic weights 2024. Electron configuration and ionisation energy: NIST Atomic Spectra Database. Family, state and electronegativity: PubChem. See Sources. Melting points, boiling points and densities are left out for now: published values differ between sources, and we will add them once each has been checked.