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Technetium (Tc). Diagram of the nuclear composition and electron configuration of an atom of technetium-98 (atomic number: 43), the most common isotope of this element. The nucleus consists of 43 protons (red) and 55 neutrons (blue). Technetium is a transition metal in group 7, period 5, and the d-block of the periodic table. It has a melting point of 2157 degrees Celsius. The transition metal trends are due to electrons filling an inner d-subshell (here, within the 4th ring), shielding the outer electrons from the increasing nuclear charge.
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