Atomic Properties of Pm
- Atomic Number of Pm
- 61
- Atomic Mass of Pm
- 145.0000 u
- Electron Configuration
- [Xe] 4f5 6s2
- Electronegativity
- 1.13
- Block
- f-block
- Group
- —
- Period
- 6
Promethium was predicted before it was securely identified. The gap at element 61 invited several premature discovery claims, but definitive evidence arrived in 1945 when Jacob Marinsky, Lawrence Glendenin, and Charles Coryell separated radioactive isotopes from uranium-fission products at Oak Ridge. They named the element for Prometheus, the mythic figure who stole fire for humanity.
Every promethium isotope is radioactive, making it the only lanthanide with no stable isotope. Tiny natural traces arise from uranium fission, but useful quantities must be produced artificially. Promethium-145 is the longest-lived known isotope at about 17.7 years; promethium-147, with a half-life near 2.62 years, has supported specialized applications.
Promethium-147 emits beta particles and has been used in thickness-measuring gauges and betavoltaic power sources. Historical luminous paints paired radioactive energy with a phosphor. The faint trail of blue light in older storytelling was therefore misleading: promethium is not a self-luminous blue metal, and any visible glow depends on conditions or a separate light-emitting material. Radiation controls are central to every use.
Its scarcity and radioactivity keep promethium out of ordinary products. Most work concerns isotope production, decay, and narrowly engineered sources.
This Luminary earns the fading-flame image through nuclear energy, not decorative fantasy. Its atoms are never staying long on geological timescales, yet their predictable decay can measure a sheet, generate a small current, and complete a periodic-table space that chemistry had pursued for decades.