The ozone story

• Heterolytic fission - both of the shared electrons go to one of the atoms and becomes negatively charged, the other becomes positively charged
• Homolytic fission - One of the two shared electrons go to each atom
• Steps in radical chain reactions:

  1. Initiation
  2. Propagation
  3. Termination
• Photodissociation

  A chemical bond is broken by photons
• Straight chain alkanes have higher boiling points than branched isomers there's more contacts between molecules and opportunities for intermolecular bonds to form.
• Permanent dipole


  Occurs when two atoms have substantially different electronegativities
• Instantaneous dipole


  Temporary dipole as the electrons within the molecule are in constant motion
• Induced dipole

  Occurs if an unpolarised molecule is next to a dipole.
• Three kinds of intermolecular bonds

  Instantaneous dipole - induced dipole - Weakest

  Permanent dipole - induced dipole

  Permanent dipole - permanent dipole - strongest
• Nucleophile

  A molecule or a negatively charged ion with a lone pair of electrons that it can donate to a positively charged atom from a covalent bond.
• Overall reaction causing ozone to break down

  X + O3 -> XO + O2

  XO + O -> X + O2

  Overall: O + O3 -> O2 + O2
• Hydrogen bonding (exam Q answer)

  1.Molecule one contains a small hydrogen atom made partially positive by being attached to a highly electronegative atom

  2.Molecuole 2 contains a highly electronegative atom with at least one lone pair which the H atom can get very close to interact with
• Hydrogen bonding

  Permanent dipole - permanent dipole
• Explain the trend in boiling point of the haloalkanes

  Increases down the group

  Larger atomic radius, larger number of electron shells

  Stronger instantaneous dipole - induced dipole forces
• Why does nucleophilic substitution happen?

  The haloalkane bond is polar

  The electronegative halogen pulls the electron away from the carbon atom