4.The first ionization energy()of d-block elements 900 850 800 6th 750 700 5th 650 4th 600 550 500 B IVB VB VIBVIB VIB IB IB The overall tendency is that values of become slightly bigger from left->right in a row,while irregular in a group. The overall tendency is that values of I1 become slightly bigger from left → right in a row, while irregular in a group. 4. The first ionization energy(I1 ) of d-block elements