Since only two of the six outer-shell electrons
of oxygen are used for this purpose, the remaining four electrons (organized into two non-bonding pairs) arrange themselves as far away from each other as possible in order to minimize repulsion between clouds of negatively charged electrons.
, which have a larger orbit and possess more energy, move to fill the spaces created.
Their atoms are smaller than their noble brethren's and therefore hold onto their outer-shell electrons
This instability is resolved when outer-shell electrons
jump from one orbit to another to fill the inner-shell vacancies.