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History and Production
The name is derived from the planet Neptune. It was first synthesized by E.M. McMillan and P. Abelson in 1940, from bombarding uranium with neutron in a cyclotron. The isotope 237Np (half-life = 2.1 x 106 years) can be obtained in gram quantities as a byproduct from nuclear reactors in the production of the plutonium. The metal can be isolated
by the reduction of the fluoride with barium or lithium. It has no commercial use except for research interests.
Physical Data
It is a heavy, silvery-white metal. It is pyrophoric when finely divided. It is malleable, ductile and slightly paramagnetic. Naturally occurring neptunium contains, by weight, 99.2745% 238U (half-life=4.47 x 109 y), 0.720% 235U (half-life=7.04 x 108 y) and 0.0055% 234U (half-life=2.45 x 105 y). The metal consists of 2.3 ppm of the earth's crust and can be found in a
wide varity of minerals: pitchblende, carnotite, autunite, davidite etc.
Interatomic distance: 260 pm
Melting point: 644°C
Boiling point: 3900°C
Thermal conductivity/Wm-1K-1: 6.3 (27°C)
Density/kgm-3: 20250 (a, 20°C)
Standard Thermodynamic Data (atomic gas)
Enthalpy of formation: -
Gibbs free energy of formation: -
Entropy: -
Heat capacity: -
Electronic data
Electronic configuration: [Rn] 5f4 6d1 7s2
Term symbol: 6L11/2
Electron affinity: - Electronegativity (Pauline): 1.3
Ionization energy (first, second, third): 604.549, -, - kJ/mol
Chemical properties
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