Promethium
[Xe] 4f⁵ 6s² · 2 · 8 · 18 · 23 · 8 · 2
The only lanthanide with no stable isotope, and one of just two light elements that lack one entirely. Less than a kilogram of promethium exists on Earth at any moment — only what spontaneous uranium fission makes.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 61
- Atomic mass
- 145 а.е.м. ≈
- Electron configuration
- [Xe] 4f⁵ 6s²
- Electrons per shell
- 2 · 8 · 18 · 23 · 8 · 2
- Block
- f-block
- Group
- no data
- Period
- 6
- Electronegativity (Pauling)
- 1.13
- Electronegativity (Allen)
- 1.09
- Atomic radius
- 236 pm
- Covalent radius
- 199 pm
- Van der Waals radius
- 236 pm
- Ionisation energy 1
- 540 kJ/mol
- Ionisation energy 2
- 1 050 kJ/mol
- Ionisation energy 3
- 2 150 kJ/mol
- Ionisation energy 4
- 3 970 kJ/mol
- Electron affinity
- 50 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- +2, +3
Physical properties
- State at 25 °C
- solid
- Density
- 7.26 g/cm³
- Melting point
- 1 315 K · 1 041.9 °C
- Boiling point
- 3 273 K · 2 999.9 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 7.13 kJ/mol
- Heat of vaporisation
- 289 kJ/mol
- Specific heat capacity
- 0.18 J/(g·K)
- Thermal conductivity
- 17.9 W/(m·K)
Mechanical properties
- Young's modulus
- 46 GPa
- Shear modulus
- 18 GPa
- Bulk modulus
- 33 GPa
- Poisson ratio
- 0.28
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 750 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 365 pm · c = 1 165 pm
Abundance
- In the crust
- 0 mg/kg
- In the ocean
- 0 mg/L
- In the universe
- 0 mg/kg
- In the human body
- 0 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 145Pm | — | 17.68 yr | ЭЗ |
| 146Pm | — | 5.51 yr | ЭЗ, β− |
| 147Pm | — | 2.62 yr | β− |
The longest-lived isotope is promethium-145 at 17.7 years. Promethium-147, half-life 2.6 years, is the one with practical uses.
Discovery
- Year of discovery
- 1945
- Discovered by
- Marinsky, Glendenin and Coryell
- Where
- USA
- Origin of the name
- after Prometheus, who stole fire from the gods
History
Box 61 was hunted for three decades, with several discoveries announced in error. Marinsky, Glendenin and Coryell isolated it in 1945 from uranium fission products within the Manhattan Project, publishing only in 1947.
Where it occurs
Essentially absent. Estimates put about 600 grams of promethium in the entire crust at any one time.
How it is produced
From spent nuclear fuel, or by neutron irradiation of neodymium. It is made in grams.
Role in living things
No biological role.
Safety
Radioactive; the main hazards are its beta radiation and the bremsstrahlung X-rays produced when that beta is absorbed.
Uses
- Self-luminous paint — it replaced radium as the less hazardous option
- Atomic batteries for pacemakers and spacecraft (historically)
- Thickness gauges in industrial process control
Curiosities
- Promethium is named after Prometheus, who stole fire from the gods — a nod to the audacity of making an element.
- Promethium lines were found in the spectrum of the star HR 465, proof that the element is being made right now.
- Promethium is the only lanthanide that cannot be found in any natural mineral.
- Promethium salts glow pale blue from their own radiation.