An organic compound is one of a category of millions of compounds containing carbon atoms bonded to hydrogen in addition to several other elements, commonly nitrogen or oxygen. All organic compounds contain carbon atoms. However, all carbon containing compounds are not organic compounds. So, a compound such as glucose (C6H12O6) is an organic compound while carbides, carbonates and cyanides (such as sodium carbonate, Na2CO3) are not organic compounds.
Organic compounds exist in such large variations because of the unique bonding properties of carbon:
Carbon atoms can form compounds containing chains (branched or straight) and rings. This is called catenation, that is, forming long chains by bonding with other carbon atoms. This is because they can form single, double and triple bonds with other carbon atoms and atoms of other elements. These bonds formed between carbon atoms and other carbon atoms as well as other elements are very strong, and hence very stable and unreactive. One reason for the formation of strong bonds by carbon is its small size. This enables the nucleus to hold on to the shared pairs of electrons strongly. The bonds formed by elements having larger atoms are much weaker.
Since carbon atoms are tetravalent, they can bond with four other atoms of carbon or a monovalent element.
For example, one carbon atom can form bonds with four monovalent fluorine atoms in tetrafluoromethane.
Note: each bonding pair of electrons is represented with a dash as shown above.
The compounds containing rings are called cyclic compounds. The number of atoms in the ring can vary, however. There are two categories of cyclic compounds- those containing a benzene ring are cyclic aromatic compounds while all others are aliphatic cyclic compounds.
This is benzene. The hexagon represents a C6H6 group- a benzene ring. Each corner of the hexagon represents a single carbon atom.
Straight (Unbranched) Chain Compounds
These compounds do not branch outwards. They can contain a variation of single, double and triple bonds.
If you observe the lines leading from each carbon atom, you will find that there are only four leading from each. This is due to the tetravalency of carbon, that is, it has four electrons to share in its valence shell, and therefore can only form four bonds.
How many bonds do each element form in organic compounds? Nitrogen forms three bonds, hydrogen forms one bond, halogens (like bromine) form one bond and carbon, as we just discussed, forms four bonds.
Branched Chain Compounds