MCQ Detailed View

A homologous series is a group of organic compounds having the same functional group, similar chemical properties, and a general formula where each successive member differs by a CH₂ unit in its molecular structure. Examples include the alkane series (CH₄, C₂H₆, C₃H₈) or alcohols (CH₃OH, C₂H₅OH, C₃H₇OH).

Members of a homologous series share the same functional group. This functional group determines their chemical reactivity. Because the functional group remains constant, all members show similar chemical properties such as reactions with acids, bases, oxidizing agents, or combustion.

The main difference between members of a homologous series is their physical properties. As the molecular mass increases by adding a CH₂ group, measurable physical characteristics like boiling point, melting point, density, viscosity, and solubility change gradually. For example, methane is a gas at room temperature, but higher alkanes like hexane are liquids, and longer chains become solids.

The functional group does not change within the series; this is what defines the series itself. Similarly, chemical properties remain almost identical because the reactive part of the molecule (the functional group) is unchanged. The differences are primarily due to increased molecular size and mass, affecting how molecules interact with each other physically (intermolecular forces).

Therefore, physical properties are not constant across the series and increase or decrease predictably with molecular weight, while chemical properties stay similar. This predictable variation in physical properties is an important principle in organic chemistry and helps classify and study large numbers of organic compounds systematically.