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 formmetallic solid (orthorombic)
Electron configuration[Rn] 54 6d1 7s2
Melting point (ºC)640
Boiling point (ºC)3902
Abundance in earth's crust (ppm)synthetic
Isotope (abundance)
Density g/cm320.2
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 atm0.060
Oxidation state+6, +5, +4, +3
Electron affinity (eV)
1st Ionization potential (eV)6.2657

Back to the Periodic Table of the Elements.