Neptunium Element Facts

General
States
Energies
Oxidation & Electrons
Appearance & Characteristics
Reactions & Compounds
Radius
Conductivity
Abundance & Isotopes

93 Np 237.0482 Neptunium

Neptunium is Radioactive.

Name: Neptunium
Type: Actinide
Density @ 293 K: 20.45 g/cm³

Discovery of Neptunium
Neptunium was the first synthetic transuranium element (elements after uranium) of the actinide series to be discovered.

Neptunium was first produced by Edwin McMillan and Philip H. Abelson in 1940 at Berkeley Radiation Laboratory of the University of California.

McMillan and Abelson bombarded uranium-238 with neutrons and they were able to show chemically that they had produced neptunium-239, which has a half-life of just 2.3 days.

A longer lived isotope neptunium-237 was discovered in 1942. Scientists A. C. Wahl and Glenn T. Seaborg bombarded uranium-238 with fast neutrons in the Berkeley 60-inch cyclotron. They isolated several hundred milligrams of neptunium and made a thorough study of its properties. ⁽¹⁾

The element is named after the planet Neptune, continuing the theme started by Martin Klaproth when he named uranium after the planet Uranus. This theme was to continue with plutonium, which follows neptunium in the actinide series.

Symbol: Np
Atomic weight: 237.0482
Atomic volume: 11.62 cm³/mol

State (s, l, g): solid
Melting point: 913 K   ( 640 ^oC)

Boiling point: 4173 K   ( 3900 ^oC)

Specific heat capacity: 0.11 J g^-1 K^-1
Heat of fusion: 3.2 kJ mol^-1
1^st ionization energy: 597 kJ mol^-1
3^rd ionization energy: kJ mol^-1

Heat of atomization: 337 kJ mol^-1
Heat of vaporization: kJ mol^-1
2^nd ionization energy: kJ mol^-1
Electron affinity: kJ mol^-1

Shells: 2,8,18,32,23,8,2
Minimum oxidation number: 0
Min. common oxidation no.: 0
Electronegativity (Pauling Scale): 1.3

Electron configuration: [Rn] 5f⁴ 6d¹ 7s²
Maximum oxidation number: 7
Max. common oxidation no.: 5
Polarizability volume: 24.8 ų

Structure: special: complex
Hardness: mohs

Color: silvery

Harmful effects:
Neptunium is harmful due to its radioactivity.

Characteristics:
Neptunium is a silvery radioactive synthetic metal. (Miniscule quantities of neptunium-237 and neptunium-239 are found in nature as a result of beta decay of uranium.)

Neptunium exists in three allotropes: it has an orthorhombic structure at normal temperatures, a tetragonal structure above 280^oC and a cubic structure above 577^oC. ⁽²⁾

Neptunium has five oxidation states (+3 to +7) producing different colors in solution:
III:   Np³⁺ (violet)
IV:   Np⁴⁺ (yellow green)
V:   NpO₂⁺ in acidic solution (green) and in alkaline solution (yellow)
VI:   NpO₂²⁺ (pink red)
VII:  Np(VII) in alkaline solution (green) or possibly in acidic conditions (brownish-red). ⁽³⁾

Uses:
Neptunium is used mainly for research purposes. When bombarded with neutrons neptunium-237 is used to produce plutonium-238 which is used for spacecraft generators and terrestrial navigation beacons. Neptunium is also used in neutron detection equipment.

Reaction with air:
Reaction with 15 M HNO₃:
Oxide(s): NpO, NpO₂, Np₂O₅
Hydride(s): NpH₂, NpH₃

Reaction with 6 M HCl:
Reaction with 6 M NaOH:
Chloride(s): NpCl₃, NpCl₄

Atomic radius: 175 pm
Ionic radius (2+ ion): 124 pm
Ionic radius (2- ion): pm

Ionic radius (1+ ion): pm
Ionic radius (3+ ion): 115 pm
Ionic radius (1- ion): pm

Thermal conductivity: 6.3 W m^-1 K^-1

Electrical conductivity: 0.8 x 10⁶ S cm^-1