Element 61 · Lanthanide
Promethium (Pm) — Element 61
Prometheus
Promethium (Pm) is a lanthanide in Period 6 (f-block) of the periodic table with atomic number 61, standard atomic weight [145] u, and ground-state electron configuration [Xe] 4f⁵ 6s². At standard temperature and pressure it is classified as a short-lived synthetic nuclide with 3 valence electrons and common oxidation states +3.
Nuclear batteries, luminous paint
What are the atomic properties and physical constants of Promethium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 61
- Standard atomic mass
- [145] u
- Chemical family
- Lanthanide
- Ground-state configuration
- [Xe] 4f⁵ 6s²
- Electrons per shell
- 2, 8, 18, 23, 8, 2
- Valence electrons
- 3
- Common ion charges / oxidation states
- +3
- Phase at STP
- Synthetic
- Pauling electronegativity
- —
- First ionization energy
- 540 kJ/mol
- Atomic radius
- 236 pm
- Melting point
- 1,042 °C
- Boiling point
- 3,000 °C
- Discovery year
- 1945
- Table coordinate
- Period 6, f-block
- Radioactivity
- Radioactive (no stable isotopes)
How are electrons arranged across Promethium’s shells?
A neutral Promethium atom contains 61 electrons distributed across 6 occupied principal energy shells ([Xe] 4f⁵ 6s²). The table below compares Promethium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Pm | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 23 e⁻ | 32 e⁻ |
| n = 5 | O | 8 e⁻ | 50 e⁻ |
| n = 6 | P | 2 e⁻ | 72 e⁻ |
Frequently Asked Questions about Promethium (Pm)
What is the atomic mass and atomic number of Promethium (Pm)?
Promethium (Pm) has atomic number Z = 61 (61 protons in its nucleus) and an IUPAC standard atomic weight of [145] u. It sits in Period 6 in the f-block and is classified as a lanthanide.
What is the ground-state electron configuration of Promethium?
The neutral ground-state electron configuration of Promethium (Z = 61) is [Xe] 4f⁵ 6s². Across its 6 occupied principal shells (n = 1 to n = 6), the electrons per shell are 2, 8, 18, 23, 8, 2, with 3 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Promethium?
Promethium commonly forms +3 oxidation states or ion charges in compounds. Its Pauling electronegativity is — and its first ionization energy is 540 kJ/mol.
When was Promethium discovered and what is it used for?
Promethium was discovered in 1945 (Prometheus). Nuclear batteries, luminous paint
How does Promethium compare to neighboring elements?
Other lanthanide elements: