Comparison of Promethium and Actinium

Attribute	Actinium ×	Promethium ×
Electronegativity (pauling scale)	1.1	-
Atomic mass (u)	227.02775	144.91276
Standard state	Solid	Solid
Oxidation states	+3	+3
Electron configuration	[Rn]7s²6d¹	[Xe]6s²4f⁵
Ionization energy (eV)	5.17	5.55
Atomic radius (van der waals) (pm)	260	236
Boiling point (K)	3471	3273
Melting point (K)	1324	1315
Density (g/cm³)	10.07	7.26
Atomic number	89	61
Group name	Actinide	Lanthanide
Discovered (year)	1899	1945
Symbol	Ac	Pm