Manganese (Mn). Diagram of the nuclear composition and electron configuration of an atom of manganese-55 (atomic number: 25), this element's most common isotope. The nucleus consists of 25 protons (red) and 30 neutrons (yellowe). 25 electrons (white) bind to the nucleus, successively occupying available electron shells (rings). Manganese is a transition metal in group 7, period 4, and the d-block of the periodic table. It has a melting point of 1246 degrees Celsius. The trends across the transition metals are due to electrons filling an inner d-subshell (here, within the 3rd ring), shielding the outer electrons from the increasing nuclear charge.