Promethium
lanthanideProperties
| Property | Value |
|---|---|
| Atomic Mass | 145 amu |
| Category | lanthanide |
| Period | 6 |
| Electron Configuration | [Xe] 4f5 6s2 |
| Electronegativity | 1.13 (Pauling) |
| Oxidation States | 3 |
| Melting Point | 1315 K (1041.8 °C) |
| Boiling Point | 3273 K (2999.8 °C) |
| Density | 7.26 g/cm³ |
| Discovered By | Charles D. Coryell, Jacob A. Marinsky, Lawrence E. Glendenin (1945) |
About Promethium
Promethium is the lanthanide that shouldn't be here — every isotope is radioactive, with the longest-lived (¹⁴⁵Pm) decaying by electron capture with a 17.7-year half-life. By the time the Earth formed 4.5 billion years ago there was already plenty around, but by now any primordial promethium has decayed roughly 250 million times over. Coryell, Marinsky, and Glendenin teased ¹⁴⁷Pm out of uranium fission products at Oak Ridge in 1945 using ion-exchange chromatography, named it for the Titan who stole fire, and the Greek roots stuck. Trace amounts do form continuously in pitchblende from spontaneous fission of ²³⁸U — somewhere around 500 grams in the entire crust at any moment. Chemically it behaves exactly like its neighbors: only the +3 state, salts that follow the lanthanide-contraction trend between Nd³⁺ and Sm³⁺. The pink solutions of Pm³⁺ glow faintly blue from their own beta radiation.
Fun Fact
Promethium is so rare on Earth that the entire planet contains only about 500 grams of it at any given time, all produced by the spontaneous fission of uranium in rocks.
Common Uses
- Beta source in betavoltaic nuclear batteries for pacemakers and remote sensors
- Phosphor-coated luminous paint for backlit dials before tritium replaced it
- Industrial thickness gauges for paper, plastic, and thin metal foils
- Portable X-ray sources powered by promethium beta-bremsstrahlung
- Reference standard for studying lanthanide spectroscopic trends
- Tracer for ion-exchange separation methodology development