The element neptunium was named after the planet Neptune. It exists in small amounts in radioactive minerals, such as aeschynite. It is formed during nuclear explosions and was first identified inside a cyclotron. At present, there are no known uses for neptunium.
Summary of properties (Np)
| Atomic weight | [237] |
| Discoverer (year) | McMillan, Edwin M. & Abelson, Philip H. (1940) |
| Natural form | metallic solid (orthorombic) |
| Electron configuration | [Rn] 5f 4 6d1 7s2 |
| Melting point (ºC) | 640 |
| Boiling point (ºC) | 3902 |
| Abundance in earth's crust (ppm) | synthetic |
| Isotope (abundance) | |
| Density g/cm3 | 20.2 |
| Van der Waals radius (pm) | 239 |
| Covalent radius (pm) | 180 |
| Electronegativity (Pauling) | 1.36 |
| Vaporization enthalpy (kJ/mol) | 337.00 |
| Enthalpy of fusion (kJ/mol) | 3.20 |
| Specific heat capacity (J/g·K) at 25ºC and 1 atm | - |
| Thermal conductivity (W/cm·K) at 25ºC and 1 atm | 0.060 |
| Oxidation state | +6, +5, +4, +3 |
| Electron affinity (eV) | |
| 1st Ionization potential (eV) | 6.2657 |
