CBSE Class 10 Answered

Dear Student

Homologous Series: Homologous series is a series of compounds which have same general molecular formula and chemical properties. But there occur variation in the physical properties. Each consecutive member differs from the next by one carbon atom and two hydrogen atoms (-CH₂ group). The compounds of a homologous series have similar chemical properties.The physical properties however show a regular gradation.

For example: 
ALKANES: General formula is C_nH_2n+2
All of these are saturated molecules. as the molecular weight gradually increses a CH₂ is increses.
Chemical properties: The chemical properties remain almost the same through out the series. As these molecules are saturated covalent hydrocarbons, they show same type of chemical reactions.

Physical properties: As we move in the series. with the increase in the CH₂ fragment, the molecular weight increases.

Most alkanes of low molecular weight are gases while the next higher molecular weight alkanes are liquids and alkanes with more than C₁₈ are colourles solids.