| Neptunium | |
| Electrons per shell | 2,8,18,32,22,9,2 |
| Electron Configuration | [Rn] 5f4 6d1 7s2 |
| Ground state | (4,3/2)11/2 |
| Atomic Volume | 11.62 cm3 mol-1 |
| Electronegativity | 1.36 |
| Magnetic ordering | No data |
 Thermal Properties |
|
| Enthalpy of Atomization | No data. |
| Enthalpy of Fusion | 9.46 kJ mol-1 |
| Enthalpy of Vaporisation | 336.6 kJ mol-1 |
| Heat Capacity | 29.46 J mol-1 K-1 |
| Thermal Conductivity | 6.3 W m-1 K-1 |
| Thermal Expansion | No data. |
| Electrical Properties |
|
| Electrical resistivity | 1.20 x 10-6 Ω m |
| Electrical conductivity | 0.0312 106/cm Ω |
| Chemical Properties |
|
| Electrochemical Equivalent | 1.7689 g Ah-1 |
| Valence Electron Potential (-eV) | 96 |
| Ionization Potential | |
 First
|
6.19 |
| Energy Levels |
|
| Lα1 (intensity 100) |
13.9441 KeV |
| Lα2 (intensity 10) |
13.7597 KeV |
| Lβ1 (intensity 38) |
17.7502 KeV |
| Lβ2 (intensity 14) |
16.84 KeV |
| Lβ3 (intensity 2) |
17.9864 KeV |
| Lβ4 (intensity 2) |
17.0582 KeV |
| Lγ1 (intensity 8) |
20.7848 KeV |
| Lγ2 (intensity 2.7) |
21.0956 KeV |
| Lγ3 (intensity 2) |
15.874 KeV |
| Ll (intensity 6) |
11.8722 KeV |
| Atomic Radii |
|
| Empirical
|
175 pm |
| Bohr Radius
|
No data. |
| Covalent Radius
|
No data. |
| Van der Waals
|
No data. |
| Triple covalent
|
116 pm |
| Metallic
|
155 pm |
| Oxidation States |
|
| Main
|
Np+5 |
| Other
|
Np+2, Np+3, Np+4, Np+6, Np+7 |
Ionisation Energies (kJ mol-1)  |
|
| M - M+ |
597 |
| Vapour Pressure |
||||||
| P (Pa) | 1 | 10 | 100 | 1K | 10K | 100K |
| T (K) | 2194 | 2437 | ||||
| Crystal Structure |
|
| Structure
|
Orthorhombic |
 |
a = 666.3 pm |
| b = 472.3 pm | |
| c = 488.7 pm | |
| α = 90° | |
| β = 90° | |
| γ = 90° | |