Stratospheric Ozone Layer
Depletion
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Page 4
Naming
Freons
As
part of the marketing plan, Du Pont developed a numbering system to refer to
the chlorofluorocarbons. Each species of CFC is given a number that can be used
to determine its structural formula. For example,
trichlorofluoromethane (CFCl3) is Freon-11. (See
CFC-11) The formula for decoding this system is simple.
Add
90 to the Freon number and interpret the three-digit result according to the
following system: the left digit is the number of carbon atoms, the middle
digit is the number of hydrogen atoms, and the right digit is the number of
fluorine atoms. Conspicuous by its absence is chlorine. All the bonding sites
that are not taken up by either fluorine or hydrogen are filled by chlorine.
For example, to determine the formula for Freon-12:
CFC -12 ---> 12+ 90 = 102
This implies:
1 Carbon
0 Hydrogen
2
To
determine the number of chlorine atoms, begin by imagining the methane building
block.
Then,
using the numbers from the formula above, fill in the information that is
derived. Finally, count the number of vacant sites. This number equals the
number of chlorine atoms. In the case of CFC-12, 1 carbon has four bonding
sites. Since there are 0 hydrogen and 2 fluorines, this leaves 2 bonding sites
(4 carbon - 2 fluorines). Chlorines fill the empty sites meaning there are two
chlorines.
