What is an homologous series? Explain with an example.

The best-known example of an homologous series is the alkanes. Alkanes are a group of saturated hydrocarbons (meaning they contain only carbon-carbon and carbon-hydrogen single bonds) with the general molecular formula CnH2n+2, where “n” represents the number of carbon atoms in the molecule. Here’s an example of an alkane homologous series:

1. Methane (CH4)
2. Ethane (C2H6)
3. Propane (C3H8)
4. Butane (C4H10)
5. Pentane (C5H12)
6. Hexane (C6H14)
7. Heptane (C7H16)
8. Octane (C8H18)
9. Nonane (C9H20)
10. Decane (C10H22)
In this series, each compound differs from the previous one by a “CH2” unit. As you move from methane to ethane, for example, you add one carbon atom and two hydrogen atoms. This pattern continues throughout the series. The systematic increase in the number of carbon and hydrogen atoms results in changes in physical properties such as boiling point, melting point, and density, as well as changes in chemical reactivity.

Another example of an homologous series is the alkenes, which are unsaturated hydrocarbons with double bonds between carbon atoms. Alkenes have the general formula CnH2n and include compounds like ethene (C2H4), propene (C3H6), and butene (C4H8). In this series, the number of carbon atoms increases by one, and the number of hydrogen atoms increases by two as you move from one member to the next.

Homologous series are essential in organic chemistry because they allow for the prediction of properties and behaviors of related compounds within the series, which simplifies the study of a wide range of organic molecules.