Element: Neptunium
General data
| Element name | Neptunium |
|---|---|
| Chemical symbol | Np |
| Atomic number Z | 93 |
| Year discovered | 1940 |
| Standard state (25°C) | Solid |
| Category | Actinide |
| Block | f |
| Atomic mass | [237] |
| CPK color | #0080FF |
Physical properties
| Melting point | 917 K (644 °C) |
|---|---|
| Boiling point | 4175 K (3902 °C) |
| Density | 20.25 g/cm³ |
Energy properties
| First ionization energy | 6.266 eV |
|---|---|
| Electron affinity | no data |
Atomic structure
| Protons | 93 (Atomic number) |
|---|---|
| Neutrons (Np-237, longest-lived isotope) | 144 |
| Electrons | 93 |
| Electron configuration | [Rn] 7s² 5f⁴ 6d¹ |
| Oxidation states | +6, +5, +4, +3 |
| Electronegativity (Pauling) | 1.36 |
| Atomic radius (van der Waals) | 221 pm |
Ionization energies - NIST ASD (93 states)
| State | Charge | Ioniz. energy (eV) | Type |
|---|---|---|---|
| Np I | 0+ | 6.265608 ± 0.000019 | measured |
| Np II | 1+ | 11.5 ± 0.4 | semi-empirical |
| Np III | 2+ | 19.7 ± 0.4 | semi-empirical |
| Np IV | 3+ | 33.8 ± 0.4 | semi-empirical |
| Np V | 4+ | 48 ± 1.9 | calculated |
| Np VI | 5+ | 65 ± 2 | calculated |
| Np VII | 6+ | 92 ± 5 | calculated |
| Np VIII | 7+ | 107 ± 5 | calculated |
| Np IX | 8+ | 121 ± 6 | calculated |
| Np X | 9+ | 136 ± 7 | calculated |
| Np XI | 10+ | 151 ± 8 | calculated |
| Np XII | 11+ | 179 ± 2.5 | calculated |
| Np XIII | 12+ | 196 ± 3 | calculated |
| Np XIV | 13+ | 233 ± 3 | calculated |
| Np XV | 14+ | 252 ± 3 | calculated |
| Np XVI | 15+ | 355 ± 3 | calculated |
| Np XVII | 16+ | 382 ± 3 | calculated |
| Np XVIII | 17+ | 408 ± 3 | calculated |
| Np XIX | 18+ | 438 ± 3 | calculated |
| Np XX | 19+ | 466 ± 4 | calculated |
| Np XXI | 20+ | 495 ± 4 | calculated |
| Np XXII | 21+ | 535 ± 4 | calculated |
| Np XXIII | 22+ | 565 ± 4 | calculated |
| Np XXIV | 23+ | 596 ± 4 | calculated |
| Np XXV | 24+ | 626 ± 4 | calculated |
| Np XXVI | 25+ | 770 ± 40 | calculated |
| Np XXVII | 26+ | 810 ± 40 | calculated |
| Np XXVIII | 27+ | 850 ± 40 | calculated |
| Np XXIX | 28+ | 880 ± 40 | calculated |
| Np XXX | 29+ | 980 ± 50 | calculated |
| Np XXXI | 30+ | 1020 ± 50 | calculated |
| Np XXXII | 31+ | 1130 ± 60 | calculated |
| Np XXXIII | 32+ | 1170 ± 60 | calculated |
| Np XXXIV | 33+ | 1280 ± 60 | calculated |
| Np XXXV | 34+ | 1360 ± 70 | calculated |
| Np XXXVI | 35+ | 1430 ± 70 | calculated |
| Np XXXVII | 36+ | 1510 ± 70 | calculated |
| Np XXXVIII | 37+ | 1590 ± 80 | calculated |
| Np XXXIX | 38+ | 1670 ± 80 | calculated |
| Np XL | 39+ | 1740 ± 90 | calculated |
| Np XLI | 40+ | 1820 ± 90 | calculated |
| Np XLII | 41+ | 1910 ± 100 | calculated |
| Np XLIII | 42+ | 1990 ± 100 | calculated |
| Np XLIV | 43+ | 2070 ± 100 | calculated |
| Np XLV | 44+ | 2140 ± 110 | calculated |
| Np XLVI | 45+ | 2230 ± 110 | calculated |
| Np XLVII | 46+ | 2310 ± 110 | calculated |
| Np XLVIII | 47+ | 2675 ± 4 | calculated |
| Np XLIX | 48+ | 2745 ± 4 | calculated |
| Np L | 49+ | 2817 ± 4 | calculated |
| Np LI | 50+ | 2894 ± 4 | calculated |
| Np LII | 51+ | 2969 ± 4 | calculated |
| Np LIII | 52+ | 3041 ± 4 | calculated |
| Np LIV | 53+ | 3181 ± 5 | calculated |
| Np LV | 54+ | 3255 ± 5 | calculated |
| Np LVI | 55+ | 3338 ± 5 | calculated |
| Np LVII | 56+ | 3413 ± 5 | calculated |
| Np LVIII | 57+ | 3718 ± 6 | calculated |
| Np LIX | 58+ | 3792 ± 6 | calculated |
| Np LX | 59+ | 3872 ± 7 | calculated |
| Np LXI | 60+ | 3947 ± 10 | calculated |
| Np LXII | 61+ | 4353 ± 12 | calculated |
| Np LXIII | 62+ | 4441 ± 15 | calculated |
| Np LXIV | 63+ | 4658 ± 19 | calculated |
| Np LXV | 64+ | 4744 ± 24 | calculated |
| Np LXVI | 65+ | 7610 ± 30 | calculated |
| Np LXVII | 66+ | 7770 ± 40 | calculated |
| Np LXVIII | 67+ | 7950 ± 40 | calculated |
| Np LXIX | 68+ | 8130 ± 50 | calculated |
| Np LXX | 69+ | 8310 ± 50 | calculated |
| Np LXXI | 70+ | 8480 ± 60 | calculated |
| Np LXXII | 71+ | 8890 ± 60 | calculated |
| Np LXXIII | 72+ | 9070 ± 70 | calculated |
| Np LXXIV | 73+ | 9270 ± 90 | calculated |
| Np LXXV | 74+ | 9450 ± 90 | calculated |
| Np LXXVI | 75+ | 9970 ± 100 | calculated |
| Np LXXVII | 76+ | 10130 ± 110 | calculated |
| Np LXXVIII | 77+ | 10300 ± 120 | calculated |
| Np LXXIX | 78+ | 10470 ± 120 | calculated |
| Np LXXX | 79+ | 11730 ± 140 | calculated |
| Np LXXXI | 80+ | 11930 ± 150 | calculated |
| Np LXXXII | 81+ | 12320 ± 160 | calculated |
| Np LXXXIII | 82+ | 12500 ± 170 | calculated |
| Np LXXXIV | 83+ | 25870 ± 190 | calculated |
| Np LXXXV | 84+ | 26300 ± 200 | calculated |
| Np LXXXVI | 85+ | 26770 ± 220 | calculated |
| Np LXXXVII | 86+ | 27210 ± 240 | calculated |
| Np LXXXVIII | 87+ | 31910 ± 250 | calculated |
| Np LXXXIX | 88+ | 32500 ± 300 | calculated |
| Np XC | 89+ | 33300 ± 300 | calculated |
| Np XCI | 90+ | 33722.2 ± 0.7 | calculated |
| Np XCII | 91+ | 132911 ± 3 | calculated |
| Np XCIII | 92+ | 135202 ± 4 | 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 (25)
| A | N | Half-life | Decay |
|---|---|---|---|
| Np-219 | 126 | 200 μs | α |
| Np-220 | 127 | 25 μs | α |
| Np-222 | 129 | 400 ns | α |
| Np-223 | 130 | 2.2 μs | α |
| Np-224 | 131 | 40 μs | α |
| Np-225 | 132 | 4 ms | α |
| Np-226 | 133 | 37 ms | α |
| Np-227 | 134 | 0.51 s | α |
| Np-228 | 135 | 61.4 s | EC/β⁺ |
| Np-229 | 136 | 4.0 min | α |
| Np-230 | 137 | 4.63 min | EC/β⁺ |
| Np-231 | 138 | 48.8 min | EC/β⁺ |
| Np-232 | 139 | 14.7 min | EC/β⁺ |
| Np-233 | 140 | 36.2 min | EC |
| Np-234 | 141 | 4.4 d | EC/β⁺ |
| Np-235 | 142 | 396.1 d | EC |
| Np-236 | 143 | 1.550×10⁵ a | β⁻ |
| Np-237 | 144 | 2.144×10⁶ a | α |
| Np-238 | 145 | 2.0993 d | β⁻ |
| Np-239 | 146 | 2.356 d | β⁻ |
| Np-240 | 147 | 61.9 min | β⁻ |
| Np-241 | 148 | 13.9 min | β⁻ |
| Np-242 | 149 | 2.2 min | β⁻ |
| Np-243 | 150 | 1.85 min | β⁻ |
| Np-244 | 151 | 2.29 min | 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