Neptunium (Np)
Actinide · f-block · period 7
Silvery, ductile radioactive metal.
Neptunium (symbol Np) is chemical element number 93, a actinide in the actinide series (f-block), period 7 of the periodic table. Its standard atomic weight is (237) and its electron configuration is [Rn] 5f4 6d1 7s2. At room temperature it is a solid, and it is radioactive. The first synthetic element beyond uranium — named after Neptune, the next planet out.
Properties
| Atomic number | 93 |
|---|---|
| Atomic mass | (237) |
| Category | Actinide |
| Block | f-block |
| Group · Period | f-block series · 7 |
| Electron configuration | [Rn] 5f4 6d1 7s2 |
| Electrons per shell | 2, 8, 18, 32, 22, 9, 2 |
| State at 25 °C | solid |
| Melting point | 912 K |
| Boiling point | 4273 K |
| Density | 20.45 g/cm³ |
| Electronegativity (Pauling) | 1.36 |
| Radioactive | Yes — no stable isotope |
| Origin | decay |
| Discovered | 1940 · McMillan & Abelson |
Key facts about Neptunium
- The first synthetic element beyond uranium — named after Neptune, the next planet out.
- Trace amounts occur in uranium ore where neutrons convert uranium to neptunium.
- Neptunium-237 could in principle be made into a bomb, so it is closely safeguarded.
- A by-product of every operating nuclear reactor.
What Neptunium is used for
Neutron-detection instruments, a feedstock for making plutonium-238, research.
Where it sits in the periodic table
Neptunium is in the actinide series, period 7, of the f-block. Its electron configuration [Rn] 5f4 6d1 7s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Neptunium on the interactive table →
Neptunium — frequently asked questions
What is Neptunium used for?
Neutron-detection instruments, a feedstock for making plutonium-238, research.
Is Neptunium radioactive?
Yes. Neptunium has no stable isotope, so every form of it is radioactive.
What is the electron configuration of Neptunium?
Neptunium has the electron configuration [Rn] 5f4 6d1 7s2, which is 2, 8, 18, 32, 22, 9, 2 electrons per shell.
What group and period is Neptunium in?
Neptunium is in the actinide series (f-block), period 7, in the f-block. Its outer shell holds 2 electrons.
Who discovered Neptunium?
Neptunium was discovered in 1940 by McMillan & Abelson.