Comparison of Uranium and Neptunium

Attribute	Uranium ×	Neptunium ×
Standard state	Solid	Solid
Electron configuration	[Rn]7s²5f³6d¹	[Rn]7s²5f⁴6d¹
Atomic mass (u)	238.0289	237.048172
Electronegativity (pauling scale)	1.38	1.36
Oxidation states	+3 +4 +5 +6	+3 +4 +5 +6
Ionization energy (eV)	6.194	6.266
Atomic radius (van der waals) (pm)	240	221
Boiling point (K)	4404	4175
Melting point (K)	1408	917
Density (g/cm³)	18.95	20.25
Atomic number	92	93
Group name	Actinide	Actinide
Discovered (year)	1789	1940
Symbol	U	Np