My Saved Article
|Atomic Number:||93||Atomic Symbol:||Np|
|Atomic Weight:||237.0482||Electron Configuration:||2-8-18-32-22-9-2|
|Melting Point:||1132oC||Boiling Point:||3818oC|
|Description:||Silvery-white radioactive metal. ;|
|Uses:||For many centuries it was used as a pigment for glass. |
Now it is
used as a fuel in nuclear reactors an in bombs.
History(Planet Neptune) Neptunium was the first synthetic transuranium
element of the actinide series discovered; the isotope 239Np was produced by
McMillan and Abelson in 1940 at Berkeley, California, as the result of
bombarding uranium with cyclotron-produced neutrons. The isotope 237Np
(half-=life of 2.14 x 10^6 years) is currently obtained in gram quantities as a
by-product from nuclear reactors in the production of plutonium.
OccurenceTrace quantities of the element are actually found in nature
due to transmutation reactions in uranium ores produced by the neutrons which
are present. Neptunium is prepared by the reduction of NpF3 with barium or
lithium vapor at about 1200C.
PropertiesNeptunium metal has a silvery appearance, is chemically
reactive, and exists in at least three structural modifications:
alpha-neptunium, orthohombic, density 20.25 g/cm^3, beta-neptunium (above 280C),
tetragonal, density (313C) 19.36 g/cm^3, gamma-neptunium (above 577C), cubic,
density (600C) 18.0 g/cm^3. Neptunium has four ionic oxidation states in
solution: Np+3 (pale purple), analogous to the rare earch ion Pm+3, Np+4 (yellow
green); NpO+ (green blue): and NpO++ (pale pink). These latter oxygenated
species are in contrast to the rare earths which exhibit only simple ions of the
(II), (III), and (IV) oxidation states in aqueous solution. The element forms
tri- and tetrahalides such as NpF3, NpF4, NpCl4, NpBr3, NpI3, and oxides fo the
various compositions such as are found in the uranium-oxygen system, including
Np3O8 and NpO2.
IsotopesFifteen isotopes of neptunium are now recognized. The O.R.N.L.
has 237Np available for sale to its licensees and for export. This isotope can
be used as a component in neutron detection instruments. It is offered at a
price of $280/g.