Skip to main content

Class 10, Science, Chapter-4, Lecture-2, Homologous Series of Organic Compounds (Notes)

TYPES OF CHAINS Formed by carbon.

  • Straight chain
  • Branched chain
  • Closed chain

SATURATED CARBON COMPOUNDS

The carbon compounds which contain only carbon-carbon covalent single bonds are called saturated carbon compound.

UNSATURATED CARBON COMPOUNDS

The carbon compounds which contain one or more carbon-carbon covalent multiple bonds are called unsaturated carbon compound.

HYDROCARBONS

The organic compounds which contain only carbon and hydrogen are called hydrocarbons.

Types of Hydrocarbons:

(i) Saturated hydrocarbons (ALKANES)

The hydrocarbons which contain only carbon-carbon covalent single bonds are called alkenes.

General Formula:  

${{\rm{C}}_n}{{\rm{H}}_{2n + 2}}$

(ii) Unsaturated hydrocarbons

(a) ALKENES

The hydrocarbons which contain one or more carbon-carbon covalent double bonds and do not contain triple bonds are called alkenes.

General Formula:  

${{\rm{C}}_n}{{\rm{H}}_{2n}}$
(b)ALKYNES

The hydrocarbons which contain one or more carbon-carbon covalent triple bonds and do not contain double bonds are called alkynes.

General Formula:  

${{\rm{C}}_n}{{\rm{H}}_{2n - 2}}$

HETEROATOM

The element that replaces a hydrogen atom from an organic compound is termed as a heteroatom.
Example:   ${\rm{Cl}}$  is the heteroatom in  ${\rm{C}}{{\rm{H}}_3}{\rm{Cl}}$

ALKYL RADICAL

A group of atoms formed by removal of one hydrogen atom from an alkane molecule which acts like a single atom in chemical reactions is termed as an alkyl radical.
General Formula: $ - {C_n}{H_{2n + 1}}$  

Example: $ - C{H_3}$   is an alkyl radical formed by removal of an H atom from CH4 molecule.

 

ALKYLE RADICAL

NAME

—CH3

Methyl

—C2H5

Ethyl

—C3H7

Propyl

—C4H9

Butyl

FUNCTIONAL GROUP

An atom or a group of atoms in an organic molecule that is responsible for the compound’s characteristic reactions and determines its properties is known as a functional group.

HOMOLOGOUS SERIES

A series of organic compounds having the same functional group and similar chemical properties in which successive members differ in their molecular formula by a $ - C{H_2}$  group is called a homologous series.

Characteristics of Homologous Series

  1. All the members of a homologous series have the same general formula.
  2. Successive members differ in their molecular formula by a $ - C{H_2}$ group.
  3. Successive members differ in their molecular mass by 14 U (unified atomic mass).
  4. All the members have similar chemical properties.
  5. Physical properties of the member change gradually.
  6. All the members of a series can be prepared by the same general method of preparation.