Promethium (Pm)
Lanthanide · Radioactive · Synthetic
Promethium is the only lanthanide with no stable isotope — every atom of it is radioactive. It exists on Earth only in vanishing traces, so all usable promethium is made in nuclear reactors.
Position on the periodic table
Atomic properties
| Atomic number | 61 |
|---|---|
| Atomic mass | 145 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f5 |
| Noble gas shorthand | [Xe] 4f5 6s2 |
| Electrons per shell | 2, 8, 18, 23, 8, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +3 |
| Electronegativity (Pauling) | 1.13 |
| Covalent radius (approx.) | 199 pm |
| First ionization energy | 540 kJ/mol |
| Electron affinity | 12.5 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 7.26 g/cm³ |
| Melting point | 1041.8 °C (1315 K) |
| Boiling point | 2999.8 °C (3273 K) |
| Appearance | metallic |
| Radioactive | Yes |
| Origin | Synthetic (lab-made) |
Electron configuration of promethium
Promethium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f5, usually shortened to [Xe] 4f5 6s2. Its electrons occupy 6 shells (2, 8, 18, 23, 8, 2), placing it in period 6 of the f-block. Explore it interactively in the electron configuration calculator.
Uses of promethium
- Luminous paint for instrument dials (historic)
- Nuclear batteries for spacecraft and pacemakers (historic/specialist)
- Thickness gauges
Biological role: None — radioactive.
Occurrence: Effectively absent from nature; produced artificially from uranium fission products.
Common compounds of promethium
PmCl3
Promethium(III) chloride
History and discovery
Discovered: 1945 — Chien Shiung Wu. Name origin: Named after Prometheus, the Titan who stole fire from the gods.
Conclusively identified in 1945 at Oak Ridge by Marinsky, Glendenin and Coryell in reactor fission products.
Safety notes
Radioactive — handled only in licensed facilities.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Promethium
1. What is the chemical symbol of Promethium?
2. What is the atomic number of Promethium?
3. Which category does Promethium belong to?
4. What is the state of Promethium at room temperature?
5. Which period of the periodic table is Promethium in?
Promethium FAQs
What is the atomic number of promethium?
Promethium's atomic number is 61 — every promethium atom has 61 protons in its nucleus.
What is the symbol for promethium?
Pm. Named after Prometheus, the Titan who stole fire from the gods.
Is promethium a metal, nonmetal, or metalloid?
Promethium is classified as a lanthanide.
What state is promethium at room temperature?
At about 25 °C, promethium is a solid. It melts at 1041.8 °C.
What is promethium used for?
Key uses include: luminous paint for instrument dials (historic); nuclear batteries for spacecraft and pacemakers (historic/specialist); thickness gauges.
Related elements
Keep working with this element
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