Recognised as Chemical element
Promethium
- Pm
- Z = 61
- lanthanide
- No stable isotope
Promethium (Pm) is element 61, a lanthanide in period 6. Its most stable isotope has mass number 145. Weights follow IUPAC standard atomic weights, 2021 revision.
Identity
SymbolPm
Mass number of the most stable isotope145this element has no stable isotope
Mass in kilograms2.4077816 × 10^-25
Categorylanthanide
GroupLanthanide/actinide series, with no group number
Period6
Blockf-block
Electrons in a neutral atom61
Neutrons in the most common isotope84≈
Electron configuration
Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f⁵ 5s² 5p⁶ 6s²ground state, subshells written in order of n
Noble gas shorthand[Xe] 4f⁵ 6s²
Electrons per shell2, 8, 18, 23, 8, 2K, L, M and outward
Electrons in the outer shell2
Unpaired electrons5Hund's rule; unpaired electrons make the free atom paramagnetic
Madelung ruleFollowedthe ground state is what the n + l filling order predicts
Quantities
Molar mass145 g/mol
Mass of one mole145 grams
Atoms in one gram4.1532005 × 10^21
Mass of one atom2.4077816 × 10^-22 g
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