Question

What do you understand by homologous series? Write with examples.

Hint:

Homologous series helps in predicting properties of unknown compounds belonging to the same group.

Answer 1

Step 1: Definition
A homologous series is a group of organic compounds having the same general formula, similar chemical properties, and successive members differing by a $-CH_{2}$ group (methylene group).
Step 2: Characteristics of Homologous Series
All compounds show similar chemical behaviour.
Physical properties vary in a regular manner (boiling point, melting point, solubility).
Each member differs from the next by $-CH_{2}$ group or 14 units of molecular mass.
They have the same functional group.
Step 3: Examples
Alkane Series: $CH_{4}$ (Methane), $C_{2}H_{6}$ (Ethane), $C_{3}H_{8}$ (Propane).
Alkene Series: $C_{2}H_{4}$ (Ethene), $C_{3}H_{6}$ (Propene).
Alcohol Series: $C_{2}H_{5}OH$ (Ethanol), $C_{3}H_{7}OH$ (Propanol).
Step 4: Importance
The concept of homologous series simplifies the study of organic chemistry because it groups compounds systematically.
Final Answer:
A homologous series is a family of organic compounds with the same functional group, general formula, and successive members differing by a $-CH_{2}$ unit. Examples: alkanes, alkenes, alcohols.