Ask A Scientist Chemistry Archive

Question:  Why is the molecular structure of ozone the way it is? It seems
that one could get a triangular arrangement, but it does not occur
in nature.
Thank you
 existing

Answer 1:
Ozone (o3) is indeed a triangular structure...however it
is not an equilateral triangle. Using the "Octet Rule"
looks like:
 
            ..
            O
          //  \
         //    \
        :O:    :O:
                ..
 
There is also another resonance structure with the double bond
on the other oxygen. The oxygen at the top of the triangle has
3 "structural pairs" (one lone pair and two sigma bonds) attached
and therefore the VSEPR model predicts that it is sp2 hybridized.
Therefore the three oxygens lie in a plane and the structure is
triangular. However, since the bottom two oxygens aren't
bonded to one another, the triangle is not equilateral.
Hope this helps,
-dr topper
 

Answer 2:
OK, I think I understand the question now....you were probably
wondering why ozone isn't an EQUILATERAL triangle (all 3 sides
equal) as opposed to the actual structure which is an ISOCELES
triangle (only 2 sides equal). This is a GREAT question!!!!!
I think I can answer it, but the answer involves molecular orbital
theory.
 
Ozone has its oxygen atoms all in a plane, so we say that each one
is sp2 hybridized. Most of the electron pairs are involved in
the bonding framework made up of those sp2 hybrids, but there are also
p orbitals above and below the plane, one residing on each oxygen.
These orbitals combine in a special way to make "delocalized"
molecular orbitals which extend over the whole molecule; these are the
"pi orbitals." There are 4 electrons available for placing in the pi
orbitals. If ozone were an equilateral triangle you would get a set of
pi orbitals which have a different shape than those you get from an
isosceles triangle. Molecular orbitals can either stabilize,
destabilize, or have no effect on, the molecule. If the molecule is
equilateral, you get one low-energy (stabilizing) orbital and
two high-energy (destabilizing) orbitals. Filling up these orbitals
gives two stabilizing electrons and two destabilizing electrons.
If however it is isosceles, you get one stabilizing, one "nonbonding"
and one destabilizing molecular orbital. Filling up these orbitals
gives two stabilizing and two nonbonding orbitals. Therefore the
isosceles triangle is a lower-energy structure. Whew! - dr topper