Neptunium

uranium ← neptunium → plutonium Pm ↑ Np ↓ —

Atomic properties Atomic number 93 Electron configuration [Rn] 5f4 6d1 7s2 Physical properties Melting point 639(3) °C (912(3) K) Boiling point 3900 °C (4175 K) Density 19.38 g cm−3 Electric resistivity 119.3 × 10−6 Ω cm (100 ­°C) Chemical properties Electronegativity 1.36 (Pauling) Ionization energy 6.2655(2) eV, 604.53(2) kJ mol−1 Atomic radii Covalent radius 190 pm Metallic radius 155 pm Ionic radius 86 pm (Np6+, Oh) 101 pm (Np4+, Oh) Thermodynamic properties Standard entropy 50.5 J K−1 mol−1 Enthalpy change of fusion 5.19 kJ mol−1 Enthalpy change of vaporization 394(25) kJ mol−1 Molar heat capacity (Cp) 29.6 J K−1 mol−1 Miscellaneous CAS number 7439-99-8 EC number 231-108-8 Where appropriate, and unless otherwise stated, data are given for 100 kPa (1 bar) and 298.15 K (25 °C).

Neptunium (symbol: Np) is a chemical element, a member of the actinoid series. All isotopes of neptunium are unstable, with half-lives of less than about two million years: any neptunium that was present at the formation of the Solar System has long since decayed, although trace amounts of neptunium are naturally formed by the capture of neutrons by uranium-238. Apart from these traces, neptunium is prepared artificially in nuclear reactors.

Neptunium was first prepared in 1939 by Edwin McMillan at the University of California Radiation Laboratory, by the neutron bombardment of uranium-238. It was named after the planet Neptune, by analogy with uranium, named after the planet Uranus.

Notes and references

Further reading

• Lemire, R. J.; Fuger, J.; Nitsche, H.; Potter, P.; Rand, M. H.; Rydberg, J.; Spahiu, K.; Sullivan, J. C., et al. Chemical Thermodynamics of Neptunium and Plutonium; Elsevier: Amsterdam, 2001. ISBN 044450379X.

External links

• WebElements