Comparison of Zirconium and Hafnium

Attribute	Hafnium ×	Zirconium ×
Atomic mass (u)	178.49	91.22
Standard state	Solid	Solid
Oxidation states	+4	+4
Electron configuration	[Xe]6s²4f¹⁴5d²	[Kr]5s²4d²
Atomic radius (van der waals) (pm)	212	186
Electronegativity (pauling scale)	1.3	1.33
Electron affinity (eV)	-	0.426
Ionization energy (eV)	6.825	6.634
Boiling point (K)	4876	4682
Melting point (K)	2506	2128
Density (g/cm³)	13.3	6.52
Atomic number	72	40
Group name	Transition metal	Transition metal
Symbol	Hf	Zr
Discovered (year)	1923	1789