Element: Promethium
General data
| Element name | Promethium |
|---|---|
| Chemical symbol | Pm |
| Atomic number Z | 61 |
| Year discovered | 1945 |
| Standard state (25°C) | Solid |
| Category | Lanthanide |
| Block | f |
| Atomic mass | [145] |
| CPK color | #A3FFC7 |
Physical properties
| Melting point | 1315 K (1042 °C) |
|---|---|
| Boiling point | 3273 K (3000 °C) |
| Density | 7.26 g/cm³ |
Energy properties
| First ionization energy | 5.55 eV |
|---|---|
| Electron affinity | no data |
Atomic structure
| Protons | 61 (Atomic number) |
|---|---|
| Neutrons (Pm-145, longest-lived isotope) | 84 |
| Electrons | 61 |
| Electron configuration | [Xe] 6s² 4f⁵ |
| Oxidation states | +3 |
| Electronegativity (Pauling) | no data |
| Atomic radius (van der Waals) | 236 pm |
Ionization energies - NIST ASD (61 states)
| State | Charge | Ioniz. energy (eV) | Type |
|---|---|---|---|
| Pm I | 0+ | 5.58187 ± 0.00004 | measured |
| Pm II | 1+ | 10.938 ± 0.02 | semi-empirical |
| Pm III | 2+ | 22.44 ± 0.08 | semi-empirical |
| Pm IV | 3+ | 41.17 ± 0.09 | semi-empirical |
| Pm V | 4+ | 61.7 ± 0.3 | semi-empirical |
| Pm VI | 5+ | 85 ± 4 | calculated |
| Pm VII | 6+ | 101 ± 5 | calculated |
| Pm VIII | 7+ | 116 ± 6 | calculated |
| Pm IX | 8+ | 138 ± 7 | calculated |
| Pm X | 9+ | 155 ± 8 | calculated |
| Pm XI | 10+ | 174 ± 9 | calculated |
| Pm XII | 11+ | 202 ± 10 | calculated |
| Pm XIII | 12+ | 229 ± 11 | calculated |
| Pm XIV | 13+ | 248 ± 3 | calculated |
| Pm XV | 14+ | 269 ± 3 | calculated |
| Pm XVI | 15+ | 430 ± 3 | calculated |
| Pm XVII | 16+ | 462 ± 3 | calculated |
| Pm XVIII | 17+ | 497 ± 3 | calculated |
| Pm XIX | 18+ | 534 ± 3 | calculated |
| Pm XX | 19+ | 569 ± 4 | calculated |
| Pm XXI | 20+ | 609 ± 4 | calculated |
| Pm XXII | 21+ | 651 ± 4 | calculated |
| Pm XXIII | 22+ | 689 ± 4 | calculated |
| Pm XXIV | 23+ | 730 ± 4 | calculated |
| Pm XXV | 24+ | 767 ± 4 | calculated |
| Pm XXVI | 25+ | 916 ± 4 | calculated |
| Pm XXVII | 26+ | 956 ± 4 | calculated |
| Pm XXVIII | 27+ | 998 ± 4 | calculated |
| Pm XXIX | 28+ | 1040 ± 4 | calculated |
| Pm XXX | 29+ | 1113 ± 4 | calculated |
| Pm XXXI | 30+ | 1158 ± 4 | calculated |
| Pm XXXII | 31+ | 1261 ± 4 | calculated |
| Pm XXXIII | 32+ | 1308.7 ± 0.6 | semi-empirical |
| Pm XXXIV | 33+ | 2251 ± 5 | calculated |
| Pm XXXV | 34+ | 2344 ± 5 | calculated |
| Pm XXXVI | 35+ | 2443 ± 5 | calculated |
| Pm XXXVII | 36+ | 2549 ± 5 | calculated |
| Pm XXXVIII | 37+ | 2652 ± 4 | calculated |
| Pm XXXIX | 38+ | 2755 ± 4 | calculated |
| Pm XL | 39+ | 2892 ± 4 | calculated |
| Pm XLI | 40+ | 2997 ± 4 | calculated |
| Pm XLII | 41+ | 3112 ± 4 | calculated |
| Pm XLIII | 42+ | 3219 ± 4 | calculated |
| Pm XLIV | 43+ | 3519 ± 4 | calculated |
| Pm XLV | 44+ | 3613 ± 4 | calculated |
| Pm XLVI | 45+ | 3718 ± 4 | calculated |
| Pm XLVII | 46+ | 3816 ± 4 | calculated |
| Pm XLVIII | 47+ | 4056 ± 4 | calculated |
| Pm XLIX | 48+ | 4166 ± 4 | calculated |
| Pm L | 49+ | 4371 ± 4 | calculated |
| Pm LI | 50+ | 4476 ± 4 | calculated |
| Pm LII | 51+ | 10115 ± 4 | calculated |
| Pm LIII | 52+ | 10378 ± 4 | calculated |
| Pm LIV | 53+ | 10671 ± 5 | calculated |
| Pm LV | 54+ | 10942 ± 5 | calculated |
| Pm LVI | 55+ | 11819 ± 5 | calculated |
| Pm LVII | 56+ | 12136 ± 5 | calculated |
| Pm LVIII | 57+ | 12532 ± 6 | calculated |
| Pm LIX | 58+ | 12797.26 ± 0.07 | calculated |
| Pm LX | 59+ | 52144.29 ± 0.06 | calculated |
| Pm LXI | 60+ | 53346.31 ± 0.14 | calculated |
Value type as given by NIST ASD: measured - from evaluated experimental data; calculated - from ab initio calculations (mostly highly ionised atoms that have not been measured; for the simplest ones, e.g. H I, the calculation is more accurate than measurement); semi-empirical - from interpolation, extrapolation or another semi-empirical method.
Photos
Isotopes (39)
| A | N | Half-life | Decay |
|---|---|---|---|
| Pm-128 | 67 | 1.0 s | EC/β⁺ |
| Pm-129 | 68 | 2.4 s | EC/β⁺ |
| Pm-130 | 69 | 2.6 s | EC/β⁺ |
| Pm-131 | 70 | 6.3 s | EC/β⁺ |
| Pm-132 | 71 | 6.9 s | EC/β⁺ |
| Pm-133 | 72 | 14 s | EC/β⁺ |
| Pm-134 | 73 | ≈ 5 s | EC/β⁺ |
| Pm-135 | 74 | 49 s | EC/β⁺ |
| Pm-136 | 75 | 107 s | EC/β⁺ |
| Pm-137 | 76 | unknown | EC/β⁺ |
| Pm-138 | 77 | 3.25 min | EC/β⁺ |
| Pm-139 | 78 | 4.14 min | EC/β⁺ |
| Pm-140 | 79 | 9.2 s | EC/β⁺ |
| Pm-141 | 80 | 20.90 min | EC/β⁺ |
| Pm-142 | 81 | 40.5 s | EC/β⁺ |
| Pm-143 | 82 | 265 d | EC/β⁺ |
| Pm-144 | 83 | 363 d | EC |
| Pm-145 | 84 | 17.7 a | EC |
| Pm-146 | 85 | 5.53 a | β⁻ |
| Pm-147 | 86 | 2.62344 a | β⁻ |
| Pm-148 | 87 | 5.368 d | β⁻ |
| Pm-149 | 88 | 53.08 h | β⁻ |
| Pm-150 | 89 | 2.698 h | β⁻ |
| Pm-151 | 90 | 28.40 h | β⁻ |
| Pm-152 | 91 | 4.1 min | β⁻ |
| Pm-153 | 92 | 5.25 min | β⁻ |
| Pm-154 | 93 | 2.68 min | β⁻ |
| Pm-155 | 94 | 41.5 s | β⁻ |
| Pm-156 | 95 | 27.8 s | β⁻ |
| Pm-157 | 96 | 10.56 s | β⁻ |
| Pm-158 | 97 | 4.8 s | β⁻ |
| Pm-159 | 98 | 1.63 s | β⁻ |
| Pm-160 | 99 | 0.73 s | β⁻ |
| Pm-161 | 100 | 730 ms | β⁻ |
| Pm-162 | 101 | 470 ms | β⁻ |
| Pm-163 | 102 | 360 ms | β⁻ |
| Pm-164 | 103 | 280 ms | β⁻ |
| Pm-165 | 104 | 0.30 s | β⁻ |
| Pm-166 | 105 | 0.23 s | β⁻ |
Data sources
- PubChem Periodic Table API - Retrieved on 29 June 2026 - licence: CC0
- IUPAC CIAAW - Abridged Standard Atomic Weights 2024 - Table version: 2024 - licence: Public domain
- NNDC Wallet Cards 2023 - Data as of 15 October 2024 - licence: Public domain
- NIST Atomic Spectra Database (ASD) - Retrieved on 29 June 2026 - licence: © U.S. Secretary of Commerce
- Images of Elements - Retrieved on 29 June 2026 - licence: CC BY 3.0