Why do the #"Group VIII"# elements have high ionization energies?
I presume you refer to the inert gases, that have high ionization energies:
Now ionization energies decrease down a Group, a column of the Periodic Table, but they INCREASE markedly across a Period, a row of the Periodic Table, from left to right as we face the Table.
As we cross the Period we progressively add an extra proton to the nucleus, which results in increased nuclear charge. Of course, we add another electron as well, however, it is added to the same valence shell. Electrons in the same valence shell shield each other very INEFFECTIVELY, with the result that atomic radii decrease markedly across the Period from left to right as we face the Table. When a new valence shell is begun, i.e. at the start of the next Period, the ionization decreases markedly, and gradually re-increases across the new Period.
Down the Group, electrons add to a new valence shell that is much more distant from the nuclear charge, and ionization energies
With the decrease in radii, and increased
Is the graphic consistent with this argument? Why? How?