4
10. Which element in each of the following sets would you expect to have the highest second
ionization energy (IE
2
)?
a) Na, K, Fe
For the second ionization energy, both Na and K remove electrons from the core
electrons with the noble gas configuration, whereas Fe would remove the 4s electron.
Na is smaller than K, therefore it would have the largest IE
2
of the three elements.
b) Na, Mg, Al
The second ionization energy of Na removes an electron from the core shell with a noble gas
configuration while Mg and Al lose 3s electrons during IE
2
. Therefore Na would have the
largest IE
2
value.
11. Until the early 1960s the group 8A elements were called inert gases. They are no longer referred
to as such, since Xe and Kr were found to react with some substances. Suggest a reason why Xe
would react with fluorine, but Ne would not.
Xe is a much larger atom than Ne, therefore it would have a much lower IE than Ne. As a
result, Xe could react with elements with large electron affinities such as F.
12. The table below gives the electron affinities in kJ/mol for group 1B and 2B elements.
a) Explain why group 1B elements have negative electron affinities, while group 2B elements have
positive values.
Group 2B elements have a complete d orbital and therefore would not be very eager to add
additional electrons to their shells. Therefore they would be expected to have positive EA.
Group 1B elements, however, have an incomplete s subshell which would readily accept an
additional electron. Therefore they would have negative EA.
b) Explain why group 1B electron affinities become more negative moving down the group.
Group 1B elements have the generic ns
1
(n–1)d
10
electron configuration and when accepting
additional electrons would experience inter-electron repulsions between the electrons on the
same energy level. Going down the group, the size of the atom increases and therefore
reduces this inter-electron repulsion. As a result, the addition of the electron is more
favored leading to a larger EA.