Neptunium (Np)
Actinide · Radioactive · Synthetic
Neptunium was the first transuranium element ever made — proof that the periodic table could be extended by human hands. It forms in every uranium reactor and is a long-lived component of nuclear waste.
Position on the periodic table
Atomic properties
| Atomic number | 93 |
|---|---|
| Atomic mass | 237 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f4 6d1 |
| Noble gas shorthand | [Rn] 5f4 6d1 7s2 |
| Electrons per shell | 2, 8, 18, 32, 22, 9, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +5 |
| Electronegativity (Pauling) | 1.36 |
| Covalent radius (approx.) | 190 pm |
| First ionization energy | 604.5 kJ/mol |
| Electron affinity | 45.9 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 20.45 g/cm³ |
| Melting point | 638.85 °C (912 K) |
| Boiling point | 4173.9 °C (4447 K) |
| Appearance | silvery metallic |
| Radioactive | Yes |
| Origin | Synthetic (lab-made) |
Electron configuration of neptunium
Neptunium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f4 6d1, usually shortened to [Rn] 5f4 6d1 7s2. Its electrons occupy 7 shells (2, 8, 18, 32, 22, 9, 2), placing it in period 7 of the f-block. Explore it interactively in the electron configuration calculator.
Uses of neptunium
- Precursor for producing plutonium-238 (spacecraft power)
- Neutron detection research
Biological role: None.
Occurrence: Trace amounts in uranium ores; essentially all is reactor-made.
Common compounds of neptunium
NpO2
Neptunium dioxide
History and discovery
Discovered: 1940 — Edwin McMillan. Name origin: Named after Neptune, the planet beyond Uranus.
Edwin McMillan and Philip Abelson created neptunium at Berkeley in 1940 by bombarding uranium with neutrons.
Safety notes
Radiotoxic, long-lived; a nuclear-waste management concern.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Neptunium
1. What is the chemical symbol of Neptunium?
2. What is the atomic number of Neptunium?
3. Which category does Neptunium belong to?
4. What is the state of Neptunium at room temperature?
5. Which period of the periodic table is Neptunium in?
Neptunium FAQs
What is the atomic number of neptunium?
Neptunium's atomic number is 93 — every neptunium atom has 93 protons in its nucleus.
What is the symbol for neptunium?
Np. Named after Neptune, the planet beyond Uranus.
Is neptunium a metal, nonmetal, or metalloid?
Neptunium is classified as a actinide.
What state is neptunium at room temperature?
At about 25 °C, neptunium is a solid. It melts at 638.85 °C.
What is neptunium used for?
Key uses include: precursor for producing plutonium-238 (spacecraft power); neutron detection research.
Related elements
Keep working with this element
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