The block of elements in the periodic table consisting of scandium, yttrium, and lanthanum together with the three periods of transition elements: titanium to zinc, zirconium to cadmium, and hafnium to mercury. These elements all have two outer s-electrons and have d-electrons in their penultimate shell; i.e. an outer electron configuration of the form (n–1)dxns2, where x is 1 to 10. See also transition elements.