Promethium (Pm): Electron Configuration, Properties and Uses
Promethium (Pm): Electron Configuration, Properties and Uses
Electron configuration [Xe] 6s2 4f5 · f-block, lanthanide series · period 6 · Ar [145]
Promethium data
- Atomic number
- 61
- Relative atomic mass
- [145]
- Group
- – (lanthanide series)
- Period
- 6
- Block
- f
- Category
- Lanthanide
- Electron configuration
- [Xe] 6s2 4f5
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f5
- Electrons per shell
- 2, 8, 18, 23, 8, 2 (K L M N O P)
- Valence electrons
- 2 (in the outer shell)
- Electronegativity (Pauling)
- no data
- First ionisation energy
- 5.55 eV
- Atomic radius (van der Waals)
- 236 pm
- State at room temperature
- Solid
- Melting point
- 1042 °C
- Boiling point
- 3000 °C
- Density
- 7.26 g/cm³
- Common oxidation states
- +3
- Discovered
- 1945
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 23 · O 8 · P 2
Orbital diagram (outer electrons)
About promethium
With atomic number 61, promethium (Pm) has 61 protons in its nucleus and 61 electrons as a neutral atom. It belongs to the lanthanide series in period 6 (f-block), usually shown below the main table. The element was discovered in 1945. Promethium is a solid at room temperature, melting at 1042 °C and boiling at 3000 °C.
Promethium electron configuration
The electron configuration of promethium is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f5, or in short [Xe] 6s2 4f5. Its electrons occupy 6 shells: K = 2, L = 8, M = 18, N = 23, O = 8, P = 2. As a lanthanide, promethium fills the 4f subshell. Its outer 6s subshell holds 2 electrons; valence electrons for this series are not assigned by the usual group rule. When it forms cations, electrons leave the outermost subshell first: Pm3+ = [Xe] 4f4.
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p6(36) → 5s2(38) → 4d10(48) → 5p6(54) → 6s2(56) → 4f5(61)
Uses of promethium
In industry and the laboratory, promethium turns up in many places, for example small nuclear batteries (Pm-147) and research; formerly luminous paint.
Safety
Promethium is radioactive. Using, storing or transporting radioactive material requires a licence from the national regulator (BAPETEN in Indonesia). Always read the safety data sheet (SDS) before working with a chemical.
Other lanthanides
Frequently asked questions
What is the electron configuration of promethium?
The electron configuration of promethium (Pm, atomic number 61) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f5, or [Xe] 6s2 4f5 in short. By shell: 2, 8, 18, 23, 8, 2.
How many valence electrons does promethium have?
Promethium has 2 electrons in its outer shell. For lanthanides and actinides, valence electrons are not assigned by the usual group rule.
Which group and period is promethium in?
Promethium is in the lanthanide series, period 6, f-block.
What is the atomic mass of promethium?
Promethium has no stable isotope, so the mass number of its longest-lived isotope, [145], is given.
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