AHL Atomic
Structure: Evidence for Subshells
Slide 6 of 20
Exceptions to the
General Trend: Shielding (screening) effect
Two exceptions: first decrease going from the second to the
third group and second decrease going from fifth to sixth
group.
That is removing the first p electron and removing the
fourth p electron.
Let’s compare Be and B in period 2:
1.They both have the
same number of shells
2.B has a bigger nuclear
charge than Be.
2. Ionization of Be involves the removal of an
electron from the sub-shell s whereas that of B from
subshell p.
Based on what we know about nuclear charge, shells and
ionization energy, we would expect B to have a higher
ionization energy…unless…
Within a shell there are different energy levels (thus
providing evidence for the existence of subshells).
The different energy levels within a shell are subshells, in this case s and p subshells.