OZONE
OZONE
lower layer of stratosphere
Delocalisation is the sharing of a pair of electrons
between three or more atoms with at least one double
bond. Delocalisation is a characteristic of electrons
in multiple bonds when there is more than one
possible position for a double bond within a molecule.
Experimental data reveals that ozone actually contains
two equal oxygen-oxygen bonds, intermediate in length
and strength between single and double bonds. So ozon
is said to have resonance, which makes the bond lengths
approximately equal.
The molecular geometry is bent or V
shaped. The greater repulsion of the lone
pair gives a bond angle of about 117o. The
electrons in the pi bond are less tightly
held so become delocalised through the
structure, giving rise to the resonance
forms. The bond order is 1.5. This means
that the bonds are intermediate in length
and strength between single and double
oxygen- oxygen bonds.
CHEMISTRY
DEPARTMENT
The bonds in ozone are between oxygen atoms only,
so they are clearly non- polar. However, the molecule
is polar which is surprising, but it can be explained by
checking the formal charges on each atom, which shows
the uneven (not homogenous) distribution of electrons
through the structure.
There are two steps of ozone cycle in ozone dissociation.
The symbol O· represents a species known as free radical
that has an unpaired electron and so is highly reactive.
• Traps heat, creating a temperature
appropriate for life.
• Blocks some of the dangerous
radiation from the sun and prevent it
from reaching the Earth.
• Acts as an oxygen source.
The first reaction produces two free radicals in gaseous
form from oxygen molecule, and this reaction is a
homolitic fission, as during homolytic fission of a neutral
molecule with an even number of electrons, two free
radicals will be generated. The reaction which starts with
the UV photons, converts ozone into a free radical (O·)
and 2 molecules of oxygen gas with a heterolitic fission
as two different particles are produced. This is the first
step and the second step in ozone depletion occurs
when ozone reacts with free oxygen radicals to produce
oxygen molecules with an exothermic reaction.
THE CLAPPER 2014 - 2015
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