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Example - Oxygen and Carbon
| Carbon needs four electrons; oxygen needs two electrons. The carbon to
oxygen "need ratio" is 4:2, which reduces to 2:1. Therefore the carbon to oxygen
atom ratio is 1:2; one carbon for two oxygens. Therefore, the formula for this compound is
CO2. Its name is carbon dioxide. |
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C |
O |
| simplified need ratio |
2 |
1 |
| atom ratio |
1 |
2 |
| formula |
CO2 |
| name |
carbon dioxide |
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· O ·
·· |
has 6 |
| needs 2 |
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| The electron dot diagram for CO2 is a little bit more involved
than the ones that we dealt with before, so think about what is involved. The carbon
needs four electrons and it is going to get them from the oxygen atoms. Each
oxygen atom needs two electrons and they will have to get them from the carbon. So the
electron dots for the carbon and oxygen, must be arranged in a way that will allow them to
accommodate the atoms they are going to bond to. Each of the oxygen atoms needs two
electrons, so the dots around the carbon are placed in such a way that it will provide two
electrons for each oxygen. The carbon, in return, needs four electrons so it will need two
electrons from each of the oxygen atoms. So the six dots around each oxygen are placed so
that two can bond to the carbon. These are brought together to give us the electron dot
diagram for CO2 which shows the distribution of electrons within this
particular molecule. This provides the carbon with a total of eight electrons and each
oxygen has a total of eight electrons. The shared electrons are counted
both for the oxygen and for the carbon. |
| Preliminary |
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O :
·· |
: C : |
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: O
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| Combined |
··
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O : : C : : O
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E-mail instructor:
Eden Francis
Clackamas Community College
©1998, 2002 Clackamas Community College, Hal Bender
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