Element: Protactinium
General data
| Element name | Protactinium |
|---|---|
| Chemical symbol | Pa |
| Atomic number Z | 91 |
| Year discovered | 1913 |
| Standard state (25°C) | Solid |
| Category | Actinide |
| Block | f |
| Atomic mass | 231.04 |
| CPK color | #00A1FF |
Physical properties
| Melting point | 1845 K (1572 °C) |
|---|---|
| Boiling point | no data |
| Density | 15.37 g/cm³ |
Energy properties
| First ionization energy | 5.89 eV |
|---|---|
| Electron affinity | no data |
Atomic structure
| Protons | 91 (Atomic number) |
|---|---|
| Neutrons (Pa-231, most abundant isotope) | 140 |
| Electrons | 91 |
| Electron configuration | [Rn] 7s² 5f² 6d¹ |
| Oxidation states | +5, +4 |
| Electronegativity (Pauling) | 1.5 |
| Atomic radius (van der Waals) | 243 pm |
Ionization energies - NIST ASD (91 states)
| State | Charge | Ioniz. energy (eV) | Type |
|---|---|---|---|
| Pa I | 0+ | 5.89 ± 0.12 | semi-empirical |
| Pa II | 1+ | 11.9 ± 0.4 | semi-empirical |
| Pa III | 2+ | 18.6 ± 0.4 | semi-empirical |
| Pa IV | 3+ | 30.9 ± 0.4 | semi-empirical |
| Pa V | 4+ | 44.3 ± 0.4 | calculated |
| Pa VI | 5+ | 72 ± 2 | calculated |
| Pa VII | 6+ | 85.1 ± 2 | calculated |
| Pa VIII | 7+ | 98.9 ± 2.1 | calculated |
| Pa IX | 8+ | 111 ± 2.2 | calculated |
| Pa X | 9+ | 137 ± 2.2 | calculated |
| Pa XI | 10+ | 153 ± 2.4 | calculated |
| Pa XII | 11+ | 187 ± 2.5 | calculated |
| Pa XIII | 12+ | 203 ± 3 | calculated |
| Pa XIV | 13+ | 292 ± 3 | calculated |
| Pa XV | 14+ | 316 ± 3 | calculated |
| Pa XVI | 15+ | 342 ± 3 | calculated |
| Pa XVII | 16+ | 369 ± 3 | calculated |
| Pa XVIII | 17+ | 395 ± 3 | calculated |
| Pa XIX | 18+ | 423 ± 3 | calculated |
| Pa XX | 19+ | 460 ± 4 | calculated |
| Pa XXI | 20+ | 488 ± 4 | calculated |
| Pa XXII | 21+ | 518 ± 4 | calculated |
| Pa XXIII | 22+ | 546 ± 4 | calculated |
| Pa XXIV | 23+ | 690 ± 40 | calculated |
| Pa XXV | 24+ | 720 ± 40 | calculated |
| Pa XXVI | 25+ | 760 ± 40 | calculated |
| Pa XXVII | 26+ | 790 ± 40 | calculated |
| Pa XXVIII | 27+ | 880 ± 40 | calculated |
| Pa XXIX | 28+ | 920 ± 50 | calculated |
| Pa XXX | 29+ | 1020 ± 50 | calculated |
| Pa XXXI | 30+ | 1060 ± 50 | calculated |
| Pa XXXII | 31+ | 1150 ± 60 | calculated |
| Pa XXXIII | 32+ | 1220 ± 60 | calculated |
| Pa XXXIV | 33+ | 1300 ± 60 | calculated |
| Pa XXXV | 34+ | 1370 ± 70 | calculated |
| Pa XXXVI | 35+ | 1450 ± 70 | calculated |
| Pa XXXVII | 36+ | 1520 ± 80 | calculated |
| Pa XXXVIII | 37+ | 1600 ± 80 | calculated |
| Pa XXXIX | 38+ | 1670 ± 80 | calculated |
| Pa XL | 39+ | 1760 ± 90 | calculated |
| Pa XLI | 40+ | 1830 ± 90 | calculated |
| Pa XLII | 41+ | 1910 ± 100 | calculated |
| Pa XLIII | 42+ | 1980 ± 100 | calculated |
| Pa XLIV | 43+ | 2060 ± 100 | calculated |
| Pa XLV | 44+ | 2130 ± 110 | calculated |
| Pa XLVI | 45+ | 2483 ± 4 | calculated |
| Pa XLVII | 46+ | 2550 ± 4 | calculated |
| Pa XLVIII | 47+ | 2620 ± 4 | calculated |
| Pa XLIX | 48+ | 2696 ± 4 | calculated |
| Pa L | 49+ | 2766 ± 4 | calculated |
| Pa LI | 50+ | 2837 ± 4 | calculated |
| Pa LII | 51+ | 2968 ± 4 | calculated |
| Pa LIII | 52+ | 3040 ± 4 | calculated |
| Pa LIV | 53+ | 3119 ± 5 | calculated |
| Pa LV | 54+ | 3193 ± 5 | calculated |
| Pa LVI | 55+ | 3488 ± 5 | calculated |
| Pa LVII | 56+ | 3558 ± 5 | calculated |
| Pa LVIII | 57+ | 3637 ± 6 | calculated |
| Pa LIX | 58+ | 3709 ± 6 | calculated |
| Pa LX | 59+ | 4077 ± 7 | calculated |
| Pa LXI | 60+ | 4161 ± 10 | calculated |
| Pa LXII | 61+ | 4370 ± 12 | calculated |
| Pa LXIII | 62+ | 4454 ± 5 | semi-empirical |
| Pa LXIV | 63+ | 7181 ± 19 | calculated |
| Pa LXV | 64+ | 7341 ± 24 | calculated |
| Pa LXVI | 65+ | 7510 ± 30 | calculated |
| Pa LXVII | 66+ | 7690 ± 40 | calculated |
| Pa LXVIII | 67+ | 7870 ± 40 | calculated |
| Pa LXIX | 68+ | 8040 ± 50 | calculated |
| Pa LXX | 69+ | 8410 ± 50 | calculated |
| Pa LXXI | 70+ | 8590 ± 60 | calculated |
| Pa LXXII | 71+ | 8780 ± 60 | calculated |
| Pa LXXIII | 72+ | 8960 ± 70 | calculated |
| Pa LXXIV | 73+ | 9460 ± 90 | calculated |
| Pa LXXV | 74+ | 9620 ± 90 | calculated |
| Pa LXXVI | 75+ | 9790 ± 100 | calculated |
| Pa LXXVII | 76+ | 9950 ± 110 | calculated |
| Pa LXXVIII | 77+ | 11100 ± 120 | calculated |
| Pa LXXIX | 78+ | 11290 ± 120 | calculated |
| Pa LXXX | 79+ | 11660 ± 140 | calculated |
| Pa LXXXI | 80+ | 11840 ± 150 | calculated |
| Pa LXXXII | 81+ | 24660 ± 160 | calculated |
| Pa LXXXIII | 82+ | 25080 ± 170 | calculated |
| Pa LXXXIV | 83+ | 25540 ± 190 | calculated |
| Pa LXXXV | 84+ | 25970 ± 200 | calculated |
| Pa LXXXVI | 85+ | 30230 ± 220 | calculated |
| Pa LXXXVII | 86+ | 30800 ± 240 | calculated |
| Pa LXXXVIII | 87+ | 31520 ± 250 | calculated |
| Pa LXXXIX | 88+ | 31971.6 ± 0.6 | calculated |
| Pa XC | 89+ | 126304.8 ± 0.7 | calculated |
| Pa XCI | 90+ | 128507 ± 3 | 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 (29)
| A | N | Half-life | Decay |
|---|---|---|---|
| Pa-211 | 120 | 4 ms | α |
| Pa-212 | 121 | 5.0 ms | α |
| Pa-213 | 122 | 5 ms | α |
| Pa-214 | 123 | 17 ms | α |
| Pa-215 | 124 | 14 ms | α |
| Pa-216 | 125 | 118 ms | α |
| Pa-217 | 126 | 3.7 ms | α |
| Pa-218 | 127 | 109 μs | α |
| Pa-219 | 128 | 55 ns | α |
| Pa-220 | 129 | 0.89 μs | α |
| Pa-221 | 130 | 5.9 μs | α |
| Pa-222 | 131 | 3.9 ms | α |
| Pa-223 | 132 | 5.3 ms | α |
| Pa-224 | 133 | 0.85 s | α |
| Pa-225 | 134 | 1.7 s | α |
| Pa-226 | 135 | 1.8 min | α |
| Pa-227 | 136 | 38.3 min | α |
| Pa-228 | 137 | 19.8 h | EC/β⁺ |
| Pa-229 | 138 | 1.55 d | EC |
| Pa-230 | 139 | 17.4 d | β⁻ |
| Pa-231 | 140 | 32740 a | α |
| Pa-232 | 141 | 1.31 d | β⁻ |
| Pa-233 | 142 | 26.975 d | β⁻ |
| Pa-234 | 143 | 6.671 h | β⁻ |
| Pa-235 | 144 | 24.4 min | β⁻ |
| Pa-236 | 145 | 9.1 min | β⁻ |
| Pa-237 | 146 | 8.7 min | β⁻ |
| Pa-238 | 147 | 2.3 min | β⁻ |
| Pa-239 | 148 | 1.8 h | 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