Organic chemistry is the branch of chemistry which deals with carbon compounds. Due to the fact carbon is able to form strong covalent bonds with itself and long chains of up to 5000 carbon atoms in length it has created a nearly infinite number of compounds. The ability for atoms to form bonds with identical atoms is called catenation.

Carbon is found in all organic compounds. Hydrogen is usually present too as carbon always creates four covalent and one hydrogen bond.

The properties of organic compounds depends on:

• The number and arrangement of carbon atoms: this determines a number of physical properties. The more carbon atoms present the higher the Van der Waal’s forces and the higher the compound’s melting point, boiling point, and viscosity. A lot of the time the carbon atoms arrange themselves in straight chains. However, shorter, branching chains off the main chain are also common. These molecules are then known as branched. It is also possible for carbon atoms, usually 6 atoms, to arrange themselves in a ring formation. This is known as a cyclic molecule.
• The functional groups: a functional group is an atom or group of atoms which dictate particular properties of a molecule. The classification of organic molecules is dependent on the dominant functional group.

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Functional groups

The table below highlights the most important functional groups present in organic molecules.

Drawing and writing organic compounds

There are a number of ways in which organic compounds can be represented.

• Structural formula showing all the covalent bonds: also known as the graphical formula or displayed formula this shows all the covalent and ionic bonds between the atoms.

• Structural formula not showing all covalent bonds: only the important bonds are shown.

• Molecular formula: this shows the number of each atom in one molecules of a compound. Different groups have their own general formula:

? Alakanes: C_nH_2n+2

? Alkenes: C_nH_2n

? Haloalkanes: C_nH_2n+1X

• Empirical formula: this is the simplest whole number ratio of the number of atoms of each element within a substance.

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Homologous series

Organic compounds which belong in the same functional group but contain a different number of carbon atoms are part of the same homologous series. Therefore, the formula of each successive member of the series increases by -C_H2–.

The sizes of the molecule increases as you ascend a homologous series which means that the boiling and melting points also increase due to the presence of stronger Van der Waal’s forces.