Neptunium (Np)

Silvery metal

Neptunium was the first element discovered beyond uranium, created in cyclotrons and nuclear reactors, and with [Rn] 5f⁴ 6d¹ 7s², neptunium-237 (half-life 2.14 million years) is the longest-lived transuranium isotope. It is a byproduct of nuclear reactors and is being researched for long-range radioisotope thermoelectric generators.

Key metrics

Density20.5g/cm³

Melting point917K

Boiling point4,273K

Electronegativity1.36Pauling

Discovery

1940discovered

Discovered by: Edwin McMillan
Reactivity profile: Radioactive and reactive
Reactivity: High
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Rn]}\; \textcolor{#a855f7}{5_{f}^{4}}\; \textcolor{#22c55e}{6_{d}^{1}}\; \textcolor{#ef4444}{7_{s}^{2}}

[Rn] 5f4 6d1 7s2

Wave function

\Psi_{\text{Np}} \approx \frac{1}{\sqrt{93!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{93}(\mathbf{r}_{93}) \right|

Probability density $|\Psi|^2$ across the Np valence shell.

Crystal structure

Orthorhombic

Lattice constantsa 1.00 · b 1.30 · c 0.90

Cell anglesα = β = γ = 90°

Coordination number—

Atoms per cell—

Atomic packing factor0.60

Physical properties

Atomic radius: 155 pm
Ionization energy: 604 kJ/mol
Electron affinity: 45 kJ/mol
Crystal structure: Orthorhombic

Oxidation states

+3+4+5+6+7

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

917 K4273 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

486.3nmNp I (blue)Blue100%

518.0nmNp I (green)Green60%

559.8nmNp IGreen40%

Dominant line 486.3 nmRange 486–560 nmTransitions 3