Neptunium
Element 93 · Actinide
Neptunium was the first element heavier than uranium to be produced artificially. It is a silvery metal that tarnishes in air and is chemically reactive, forming compounds in oxidation states from +3 to +7, with +5 the most stable in solution. It is radioactive, decaying by alpha emission with a half-life of about 2.1 million years for neptunium-237. Its main practical role is as a precursor for making plutonium-238 used in deep-space power sources.
Key facts
| Atomic number | 93 |
|---|---|
| Atomic weight | [237] |
| Category | Actinide |
| Group / Period | — / 7 |
| Block | f |
| Electron configuration | [Rn] 5f4 6d1 7s2 |
| Common oxidation states | +5, +6, +4, +3 |
| State at STP | Solid |
| Electronegativity | 1.36 |
| Density | 20.45 g/cm3 |
| Melting point | 639 °C |
| Boiling point | 4174 °C |
Occurrence
Neptunium does not occur in useful amounts naturally; trace quantities form in uranium ores by neutron capture. It is produced synthetically by irradiating uranium-235 in nuclear reactors.
Applications
Precursor for plutonium-238 used in radioisotope thermoelectric generators
Target material for producing heavier transuranium elements
Research in actinide chemistry
Common compounds
- Neptunium dioxide (NpO2)
- Neptunyl nitrate (NpO2(NO3)2)
- Neptunium tetrafluoride (NpF4)
Neptunium was discovered in 1940 by Edwin McMillan and Philip Abelson at Berkeley and named after the planet Neptune, the next planet beyond Uranus.
Data source: IUPAC standard atomic weights 2021