Comparison of Cerium and Neptunium

Attribute	Neptunium ×	Cerium ×
Atomic mass (u)	237.048172	140.116
Standard state	Solid	Solid
Oxidation states	+3 +4 +5 +6	+3 +4
Electron configuration	[Rn]7s²5f⁴6d¹	[Xe]6s²4f¹5d¹
Atomic radius (van der waals) (pm)	221	235
Electronegativity (pauling scale)	1.36	1.12
Electron affinity (eV)	-	0.5
Ionization energy (eV)	6.266	5.539
Boiling point (K)	4175	3697
Melting point (K)	917	1071
Density (g/cm³)	20.25	6.77
Atomic number	93	58
Group name	Actinide	Lanthanide
Symbol	Np	Ce
Discovered (year)	1940	1803