AHL Atomic
Structure: Evidence for Subshells
Slide 11 of 20
Hund’s Rule and
Orbital Stabilities
Now you know why in the Aufbau principle each orbital is
first half filled until all orbitals in that
sub-shell are half filled, and then electrons are paired.
This is a statement of Hund’s rule.
So as far as stabilities of orbitals and subshells are
concerned, in general,
1. An orbital is more stable when occupied by a single
electron
2. (i) A
half-filled subshell (containing only unpaired) electrons is more
stable than either one that is less than half-filled or one that
contains a combination of unpaired and paired electrons
(ii)
A completely filled subshell
(containing only paired) electrons is more stable than
either one that is less than half-filled or one that contains a combination of
unpaired and paired electron