transition element

A transition element is an element whose atom has an incomplete d-sub-shell, or which gives rise to a cation or cations with an incomplete d-sub-shell. The First Transition Series of elements is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu. The Second and Third Transition Series are similarly derived: these include the lanthanoids (lanthanides) and actinoids (actinides) respectively which are designated inner (or f) transition elements of their respective Periods in the Periodic Table.