Neptunium (Np): Electron Configuration, Properties and Uses
Neptunium (Np): Electron Configuration, Properties and Uses
Electron configuration [Rn] 7s2 5f4 6d1 · f-block, actinide series · period 7 · Ar [237]
Neptunium data
- Atomic number
- 93
- Relative atomic mass
- [237]
- Group
- – (actinide series)
- Period
- 7
- Block
- f
- Category
- Actinide
- Electron configuration
- [Rn] 7s2 5f4 6d1
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f4 6d1
- Electrons per shell
- 2, 8, 18, 32, 22, 9, 2 (K L M N O P Q)
- Valence electrons
- 2 (in the outer shell)
- Electronegativity (Pauling)
- 1.36
- First ionisation energy
- 6.266 eV
- Atomic radius (van der Waals)
- 221 pm
- State at room temperature
- Solid
- Melting point
- 644 °C
- Boiling point
- 3902 °C
- Density
- 20.25 g/cm³
- Common oxidation states
- +6, +5, +4, +3
- Discovered
- 1940
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 32 · O 22 · P 9 · Q 2
Orbital diagram (outer electrons)
About neptunium
Neptunium is a chemical element with the symbol Np and atomic number 93. It belongs to the actinide series in period 7 (f-block), usually shown below the main table. The element was discovered in 1940. It is named after the planet Neptune. Neptunium is a solid at room temperature, melting at 644 °C and boiling at 3902 °C.
Neptunium electron configuration
The electron configuration of neptunium is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f4 6d1, or in short [Rn] 7s2 5f4 6d1. Its electrons occupy 7 shells: K = 2, L = 8, M = 18, N = 32, O = 22, P = 9, Q = 2. As an actinide, neptunium fills the 5f subshell. Its outer 7s subshell holds 2 electrons; valence electrons for this series are not assigned by the usual group rule. This is an exception to the Aufbau rule: the usual filling order predicts [Rn] 7s2 5f5, but the 5f and 6d subshells are so close in energy that electrons occupy 6d. When it forms cations, electrons leave the outermost subshell first: Np3+ = [Rn] 5f4.
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p6(36) → 5s2(38) → 4d10(48) → 5p6(54) → 6s2(56) → 4f14(70) → 5d10(80) → 6p6(86) → 7s2(88) → 5f4(92) → 6d1(93)
Uses of neptunium
The main uses of neptunium include producing Pu-238 and neutron detectors; neptunium forms as a reactor by-product.
Safety
Neptunium is radioactive. Using, storing or transporting radioactive material requires a licence from the national regulator (BAPETEN in Indonesia). Always read the safety data sheet (SDS) before working with a chemical.
Other actinides
Frequently asked questions
What is the electron configuration of neptunium?
The electron configuration of neptunium (Np, atomic number 93) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f4 6d1, or [Rn] 7s2 5f4 6d1 in short. By shell: 2, 8, 18, 32, 22, 9, 2.
How many valence electrons does neptunium have?
Neptunium has 2 electrons in its outer shell. For lanthanides and actinides, valence electrons are not assigned by the usual group rule.
Which group and period is neptunium in?
Neptunium is in the actinide series, period 7, f-block.
What is the atomic mass of neptunium?
Neptunium has no stable isotope, so the mass number of its longest-lived isotope, [237], is given.
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