From Citizendium, the Citizens' Compendium
Hafnium is a chemical element, having the chemical symbol Hf. Its atomic number (the number of protons) is 72. It has a standard atomic weight of 178.49 g•mol −1 and is a solid in its elemental form.
Hafnium is considered a member of the "Transition metal" class of elements. At a pressure of 101.325 kPa, it has a boiling point of 4,603°C and a melting point of 2,233 °C.