Promethium
Atomic Data
| Atomic Number | 61 |
| Symbol | Pm |
| Atomic Weight | 145 u |
| Density (STP) | 7.26 g/cm³ |
| Melting Point | 1041.85 °C (1315 K) |
| Boiling Point | 2999.85 °C (3273 K) |
| Electronegativity | 1.13 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f5 5s2 5p6 6s2 |
| Oxidation States | +3 |
| Phase at STP | Solid |
| Category | Lanthanoid |
| Period / Group | 6 / None |
| CAS Number | 7440-12-2 |
Electron Configuration
[Xe] 4f5 6s2
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 5 | 51 |
| O | 5 | 5s | 2 | 53 |
| O | 5 | 5p | 6 | 59 |
| P | 6 | 6s | 2 | 61 |
| Total | 61 | 61 | ||
Isotopes of Promethium
Promethium has two naturally occurring stable isotopes. The most abundant is ¹⁴⁵Pm, comprising None% of all naturally occurring Promethium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Promethium-145 | ¹⁴⁵Pm | 61 | 84 | trace | Stable |
| Promethium-147 | ¹⁴⁷Pm | 61 | 86 | trace | Stable |
Abundance & Occurrence
Promethium is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Radioactivity: all isotopes: Promethium has no stable isotopes; all are radioactive. Pm-147 (t½ = 2.6 years, beta emitter) is the principal commercial isotope and requires handling as a radioactive material under licence.
- Beta radiation: Pm-147 is a moderate-energy beta emitter; external skin dose is of moderate concern, but ingestion or inhalation of promethium presents the greater internal dose hazard: airborne particulate must be contained.
- Controlled area working: All promethium work must take place in a radiologically controlled area with appropriate contamination monitoring, personal dosimetry, and waste management.
- Natural absence: Promethium does not occur in nature in macroscopic quantities; it is always a produced material, and quantities in use are tightly regulated and inventoried under national radiation protection regulations.
Promethium in the Real World
Real-World Uses
- Radioisotope power sources: Promethium-147 (t½ = 2.6 yr) beta particles are used in thin-film betavoltaic nuclear batteries that powered early cardiac pacemakers and guided missile systems; compact long-life power sources for remote sensors remain a research interest.
- Thickness gauging: Pm-147 beta sources are used in precision industrial thickness gauges for measuring sheet metal, paper, plastic film, and textile thickness during continuous manufacturing, exploiting beta-particle attenuation through the material.
- Scientific research: As the only naturally absent element between bismuth and plutonium, promethium is studied to understand lanthanide chemistry, nuclear structure, and the s-process of nucleosynthesis in stars.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
Has promethium ever been used for anything?
Promethium-147 has been used in promethium-powered atomic batteries (betavoltaic devices) for pacemakers and guided missile guidance systems during the Cold War era, before lithium batteries became standard. It has also been used in luminescent paint for instrument dials (as a replacement for radium) and in some thickness-measuring gauges. Its radioactivity limits practical applications.
Why is promethium radioactive?
All isotopes of promethium are radioactive because, like technetium (element 43), promethium's position in the periodic table at atomic number 61 means no stable nucleus exists: the nuclear binding energy for any combination of 61 protons and neutrons does not produce stability. The most stable isotope, Pm-145, has a half-life of only 17.7 years, so any primordial promethium has long since decayed.
How was promethium discovered?
Promethium was definitively identified in 1945 by Jacob Marinsky, Lawrence Glendenin, and Charles Coryell at Oak Ridge National Laboratory while analysing uranium fission products from a nuclear reactor. They isolated it by ion exchange chromatography. The element was named after Prometheus, the Titan of Greek mythology who stole fire from the gods, symbolising the nuclear fire used in its discovery.
Does promethium occur naturally on Earth?
Traces of promethium-147 and promethium-145 have been detected in uranium ores, produced by spontaneous fission of uranium and neutron capture processes. However, the amounts are extraordinarily small: estimated at about 572 grams of Pm-147 in Earth's entire crust at any given moment. Effectively, all useful quantities of promethium are produced artificially in nuclear reactors.