Organic Chemistry

The word "organic" was introduced by Berzelius in 1780 to introduce chemicals which were obtained from living sources.

Organic chemistry has long been regarded as a separate and unique branch of chemistry, organic chemistry is the body of knowledge which is concerned with the physical and chemical properties of the broad group of carbon compounds containing hydrogen and one or more additional elements like oxygen, nitrogen, sulphur  etc. However, compounds of carbon containing only carbon and oxygen like CO, CO₂, CO₃^-2 are not studied under organic chemistry. Similarly, compounds containing carbon and nitrogen are not considered to be organic compounds.

To understand organic chemistry, knowledge of valency of atoms is essential.
Valency of different atoms:
Atom            Valency
 H                      1
 O                      2
 N                      3
 C                      4
 S                 2, 4 or 6
Carbon atom has an unique property by the virtue of which it forms regular covalent bonds with other carbon atoms. This property of carbon atom is known as catenation. Due to tetravalency. It is able to from stable C-C bond and multiple bonds like C=C, C≡C, C=S, C≡N etc.