Question

Why does the effective nuclear charge increase from the left to right in the periodic table?

Answer 1

Within a block, the extra e's are put into orbits in an existing shell, at the same distance as the v. e's that were in the previous element.

E's that are 'next to' each other like that can't shield each other from the nucleus's charge.

Only the e's between them and the nucleus can cancel out some of the charge they feel.

As you go up the row, add more e's in that outer shell, you aren't adding anything in between them and the nucleus, but your adding an extra proton to that nucleus, the charge of which doesn't get really get shielded.

So all the outer e's feel more pull and it's the pull on the outermost v.e's that Zeff measures.