Homologous Series

1. Check the functional group. 2. Compare the general formula. 3. See whether successive compounds differ by CH₂. 4. Conclude whether they form a homologous series.

Write three consecutive members vertically to show the CH₂ difference clearly, such as CH₄, C₂H₆, and C₃H₈.

A common wrong answer is to call any set of related compounds a homologous series. Without the CH₂ difference and same functional group, the answer is incomplete.

A homologous series is a family of organic compounds with the same functional group and the same general formula, where successive members differ by a CH₂ group.

A homologous series is a family of organic compounds with the same functional group and the same general formula, where successive members differ by a CH₂ group. Members of the same homologous series have the same general formula, the same functional group, and a CH₂ difference between successive compounds. Methanol, ethanol, and propanol form a homologous series because each has the -OH group and each next member differs by CH₂.

Members of a homologous series have similar chemical properties because they share the same functional group. Their physical properties show a gradual change as molecular mass increases. This idea helps students organise carbon compounds into families instead of learning them as isolated names. Members of the same homologous series have the same general formula, the same functional group, and a CH₂ difference between successive compounds. Methane, ethane, and propane belong to the alkane series. Each next member has one extra CH₂ unit, so they form a homologous series with similar chemical behaviour. Questions may ask you to identify a series, state the common difference, or explain why members behave similarly. A common wrong answer is to call any set of related compounds a homologous series. Without the CH₂ difference and same functional group, the answer is incomplete.