Explain each of the following observations using principles
of atomic structure and/or bonding
d) Boron has a lower first-ionization energy than
beryllium.
Be (1s2)(2s2)
Z* = 4 – (2 · 0.85 + 1 · 0.35) = 1.95
B (1s2)(2s2,2p1)
Z* = 8 – (2 · 0.85 + 2 · 0.35) = 2.6
We would expect from Z* arguments that it
should require more energy to remove the first electron
in boron compared to beryllium. However, the electron
that is removed from boron in in the 2p level
which is higher in energy compared to the 2s
level, therefore it is easier to remove. Recall that Z*
for the Group IA metals (after Li) are effectively the
same value, yet we all know the first ionization energy
for the valence electron in Cs is easier to remove than
the valence electron in sodium because the electron is
located in a higher energy level.