Most organic compounds contain C, N and O and these elements bond in a specific manner:
Carbon has 4 valence e-, all of them
can be bonded
Nitrogen has 5 valence e-, 2 are
paired, 3 are left to bond
Carbon typically forms 4 bonds
Nitrogen forms 3 bonds
Oxygen has 6 valence e-, 4 are
paired, 2 are left to bond
Oxygen forms 2 bonds
*We find the number of valence electrons by counting left to right on the periodic table for the row that contains
C, N or O – the elements we are interested in.
Representative compounds:
Carbon Containing Compounds
Nitrogen Containing Compounds
Oxygen Containing Compounds
We see that in every case, C has 4 bonds, N has 3 bonds, O has 2 bonds. Let’s look at a large organic
compound that has C, N and O in it:
In every case the bonding rules are met. To save time
drawing structures, we often do not show the bonded Hs
and instead write CH to indicate the carbon at a specific
spot in a compound is bonded to an H as well.
Because C behaves so reproducibly and forms 4 bonds,
we can use line diagrams to represent organic
structures. Every vertex (intersection of 2 lines) is a
carbon atom and it is assumed that C forms 4 bonds
At the highlighted vertex where two bonds meet there is
a CH2, a carbon atom with two Hs attached.
You may notice that there are a variety of different groups on the structure – they are referred to as “functional
groups” because they react differently and give the molecule different properties. Organic chemistry is like a
lego set where you can add new toys.