Could somebody kindly explain the following phenomenon:
The energy separation E4s-E3d increases slowly with atomic number up until element 30 (zinc), whereupon it increases very rapidly. For the elements up to zinc, the 4s energy decreases very slowly; thus the increase in the 4s-3d energy difference is due mostly to a more rapid decrease in the 3d energies. This general trend continues beyond zinc but becomes exaggerated as 4p electrons are added.
What I don't get is, why there is no significant energy change of 3d from Sc to Cu, but a sudden decrease from Zn