A homologous series is a group of organic compounds that have the same functional group, similar chemical properties, but differ by a constant unit in molecular formula, usually CH₂. Members of a homologous series show a gradual change in physical properties such as boiling point and melting point.

• Compounds in the series have the same general formula.
• They have similar chemical properties due to the same functional group.
• They differ by a CH₂ unit from one member to the next.
• Physical properties like melting point, boiling point, and density change gradually along the series.
• Their members show a trend in reactivity based on the size and structure of the molecule.
• Each successive member differ by an increase in 14 in their atomic masses

A functional group is a specific atom or group of atoms in an organic molecule responsible for its characteristic chemical properties. For example, -OH in alcohols, -COOH in carboxylic acids, or -CHO in aldehydes.

Note: R and R' - represents an alkyl group

An alkyl group is a group of carbon and hydrogen atoms derived from an alkane by removing one hydrogen atom. They have a general molecular formula of \(C_nH_{2n+1} \). Alkyl groups are often represented by the symbol R– and act as substituents in larger organic molecules. They are named by replacing the “-ane” ending of the parent alkane with “-yl”. For example, CH₃– is called methyl, and C₂H₅– is called ethyl. Alkyl groups are important because they determine the branching and structure of organic compounds.

Alkanes are saturated hydrocarbons containing only single C–C bonds. They have a general molecular formula of \(C_nH_{2n+2} \). They are generally unreactive except in combustion and substitution reactions. Their chemical and physical properties show gradual trends as the carbon chain length increases.