## 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.
 · ·  C  · · has 4 needs 4
 C O simplified need ratio 2 1 atom ratio 1 2 formula CO2 name carbon dioxide
 ·· ·  O  · ·· has 6 needs 2

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 ··    O  : ·· :  C  : ·· :  O    ··
 Combined ··                ·· O : : C : : O ··               ··

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