Molecular bonds are made when negatively
charged electrons from one nucleus are attracted to the positively charged
nuclei of another atom, and the electrons are then shared between nuclei. In
the case of molecular oxygen, four electrons are shared between the two nuclei,
leaving eight unpaired electrons distributed equally between the two nuclei.
Electrons are repulsed by each other, and the unpaired electrons distribute
themselves as far away from the shared electrons and each other as possible,
minimizing the energy of the molecule and resulting in a bond order of two.
In ozone, the four "shared" electrons
aren't shared across two nuclei, but across three. Formally, it leads to a bond
order of 1.5 and a resonant structure. Physically this means that six electrons
are vying for space in between three nuclei that are packed in a bent shape.
The electrons are very unhappy (high energy) to be in close proximity, but this
arrangement is its lowest possible energy arrangement, filling the lowest
energy molecular orbitals and allowing non-bonded electrons to spread out as
much as possible.
The high potential energy resulting from the
proximity of electrons makes the bond unstable.So when ozone encounters any
molecule that looks like it might vaguely like to take an oxygen atom (and its
electrons with it), the molecule gladly busts apart.