93
237.00
Np
Neptunium
Identification
CAS Number: 7439-99-8
Discovery Year: 1940
Discoverer: E.M. McMillan, P.H. Abelson
Discovery Location: United States
Properties
Atomic Dimensions
Atomic Radius: 175 pm →
Atomic Radius (Rahm): 281 pm
Covalent Radius: 190 pm →Van der Waals Radius: 239 pm
Atomic Volume: 21.1 cm³/mol
Lattice Constant: 4.72 Å
Thermodynamics
Melting Point: 913 K →Boiling Point: 4175 K →Heat of Fusion: 9.6 kJ/mol →Heat of Vaporization: 336 kJ/mol →
Heat of Formation: 464.8 kJ/mol
Electronic Structure
Electron Config: [Rn] 5f4 6d 7s2
Block: f
Period: 7 →Electronegativity: 1.3 →Oxidation States: +3, +4, +5, +6
Abundance & Geochemistry
Goldschmidt Class: synthetic
About
Radioactive metallic transuranic element, belongs to the actinoids. Np-237, the most stable isotope, has a half-life of 2.2*10^6 years and is a by product of nuclear reactors. The other known isotopes have mass numbers 229 through 236, and 238 through 241. Np-236 has a half-life of 5*10^3 years. First produced by Edwin M. McMillan and P.H. Abelson in 1940.
Isotopes
Np-236 236 ☢ 1.53e+5 a
Np-237 237 ☢ 2.14e+6 a