Hello friends, I noticed from Wikipedia the following information: Atomic radii: 4th period(only d-block elements): Sc:160 pm Ti : 140 pm V : 135 pm Cr : 140 pm Mn: 140 pm Fe : 140 pm Co : 135 pm Ni : 135 pm Cu :135 pm Zn : 135 pm Normally across the period atomic radii should decrease. But d-block elements do not follow this trend. It increases From V to Cr and them remains constant and decreases and remains constant again. So they show horizontal similarities too.. Can some one explain me this strange trend? More stranger trend is of f-block elements.. They don't change their radii at all if we go across the period!!!