Why do the #"Group VIII"# elements have high ionization energies?

1 Answer
Feb 17, 2017

Well, #"Group VIII+"# elements have a higher nuclear charge, #Z#...........


I presume you refer to the inert gases, that have high ionization energies:

#"Inert gas"# #+Deltararr"Inert gas cation + "e^(-)#

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 #"decrease"# accordingly.

With the decrease in radii, and increased #Z#, the ionization energy INCREASES progressively across the Period, with the inert gases, formally Group VIII or Group 18, (with the highest nuclear charge on the Period) having the highest ionization energy.


Is the graphic consistent with this argument? Why? How?