Periodic TablePromethium (Pm)
Promethium is a lanthanide with atomic number 61, in period 6, in the f-block of the periodic table. Its atomic mass is 145 u and its electron configuration is [Xe] 4f⁵ 6s². Solid at 25 °C.
Key facts
| Atomic number | 61 |
|---|---|
| Atomic mass | 145 u |
| Category | Lanthanide |
| Period | 6 |
| Group | f-block, no group number |
| Block | f |
| Electron configuration | [Xe] 4f⁵ 6s² |
| Electrons per shell | 2, 8, 18, 23, 8, 2 |
| Electronegativity (Pauling) | --- |
| Oxidation states | +2, +3common in bold |
| State at 25 °C | Solid |
| Melting point | 1315 K1041.85 °C |
| Boiling point | 3273 K2999.85 °C |
| Density | 7.264 g/cm³ |
Atomic properties
| First ionization energy | 5.582 eV |
|---|---|
| Electron affinity | 50 kJ/mol |
| Atomic radius | 183 pm |
| Covalent radius | 199 pm |
| Van der Waals radius | 236 pm |
| Common ions | Pm³⁺ |
| Protons, neutrons, electrons | 61, 84, 61 |
Physical and thermal properties
| Molar volume | 20.23 cm³/mol |
|---|---|
| Heat of fusion | 7.7 kJ/mol |
| Heat of vaporization | 290 kJ/mol |
| Specific heat | --- |
| Thermal conductivity | 15 W/(m·K) |
| Thermal expansion | 1.1 × 10⁻⁵ K⁻¹ |
| Mohs hardness | --- |
| Young’s modulus | 46 GPa |
| Crystal structure | Simple hexagonal |
| Magnetic type | Paramagnetic |
Identification and history
| CAS number | 7440-12-2 |
|---|---|
| Latin name | Promethium |
| Discovered by | J. Marinsky, L. Glendenin, C. Coryell · 1945 |
| Named by | Grace Mary Coryell · 1945 |
Natural isotopes
Promethium has no stable isotopes: every isotope is radioactive.
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
See Promethium in the app
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