Manganese, Mn (atomic number Z = 25; relative atomic mass A r = 54.938) is an element of the VIIb group of the periodic table of elements, together with technetium and rhenium. It belongs to 16 the first series of d-block transition elements which also contains titanium, vanadium, chromium, nickel, and copper. Because of their electron configuration, transition elements have some characteristic properties: they are all metals; they exist in a variety of oxidation states; and they form many coloured and paramagnetic compounds. Several transition elements have an important role in biological systems.