Lecture 10: Water and Ozone

Read section 4.4 from your textbook.

Water and Ozone, Structure and Bonding

As always, our first step is to construct a Lewis structure for each of these molecules.



VSEPR gives us the structure.



Each molecule has a C2 axis and 2 vertical planes. This puts them in the C2v point group.



Let's look at sigma bonding first.
  • For water, we need to make 2 group orbitals from the hydrogen atomic 1s orbitals.
  • For ozone, we make the 2 group orbitals from the terminal oxygen 2s orbitals.
  • In each case, one orbital will have 0 nodes and the other, higher energy one will have 1 node.




Note that the lower energy orbital (group 1) transforms like A1 in the C2v group and the higher energy group orbital (group 2) transforms like B2. What oxygen orbitals will this interact with? Let's look at the symmetry.



From the symmetry, we see that
  • both the 2pz and the 2s orbitals on the central oxygen will interact with group 1 (A1)
  • the the 2py orbital will interact with group 2 (B2)
  • the 2px doesn't have the correct symmetry for sigma bonding


Let's combine the 2 A1 symmetry orbitals on the central oxygen (2s and 2pz) with the group orbital with that symmetry. Combining 3 orbitals must give us 3 molecular orbitals: 1, 2, and 3.



Now we can combine the orbitals with B2 symmetry: 2py on the central oxygen with group orbital 2. Combining 2 orbitals will give us 2 molecular orbitals.



In water, there is a remaining 2px orbital on the oxygen that can't combine with any other orbital. This becomes a non-bonding molecular orbital. We wind up with a total of 6 molecular orbitals.
  • The bottom 2 orbitals are strongly bonding.
  • The top 2 orbitals are strongly antibonding.
  • The middle two orbitals are pretty much non-bonding. These can be represented by the oxygen lone pairs in the Lewis structure of water.




What about ozone? The 2px orbital on the central oxygen has the correct symmetry to combine with a group orbital made up of 2px orbitals on the two terminal oxygen atoms.



These 2 orbitals can combine to form 2 pi symmetry molecular orbitals. The remaining orbitals on the terminal oxygens (O1(2py), O1(2pz, O3(2py), and O3(2pz) are non-bonding.



Chemistry of Water

  1. Acid-Base Chemistry


  2. Reaction with Active Metals


  3. Water as a Lewis Base


  4. Water as a Nucleophile


  5. Water as an Electrophile


Chemistry of Ozone

  1. Photolysis


  2. Reactions with Alkenes


  3. Ozone as an Oxidation Agent