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Hafnium (Hf). Diagram of the nuclear composition and electron configuration of an atom of hafnium-178 (atomic number: 72), the most common isotope of this element. The nucleus consists of 72 protons (red) and 106 neutrons (blue). Hafnium is a transition metal in group 4, period 6, and the d-block of the periodic table. It has a melting point of 2233 degrees Celsius. The trends across the transition metals are due to electrons filling an inner d-subshell (here, within the 5th ring), shielding the outer electrons from the increasing nuclear charge.
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