A homologous series is a series of compounds with similar chemical properties where each member differs from the next by a CH2 group. The key characteristics of a homologous series are: 1) Each member can be represented by a common chemical formula that differs by CH2. 2) Members are prepared by a common method. 3) Members have the same chemical properties. 4) Each member differs from the next by one CH2 group which has a mass of 14.

1.  A series of compounds with similar chemical
properties, in which members differ from one
another by additional CH2 group, is called a
homologous series.
Homologous Series

2. Members of the
same homologous
series can be
prepared through
one common
method.
Members of the
homologous
series have the
same chemical
properties.
Every member in
the homologous
series can be
represented by a
common formula.
Every member
differ from
others by the
group -CH2-
which has the
relative mass 14
• Four characteristics of
homologous series

3. Every member in the homologous
series can be represented by
a common formula.
For example:
 Alkane: CnH2n+2
 Alkene: CnH2n
 Alcohol: CnH2n+1OH
 Carboxylic acid : CnH2n+1COOH
 Ester: CnH2n+1COOCmH2m+1

4. Every member differ from others
by the group -CH2- which has the
relative mass 14.
For example:

5. Members of the same homologous
series can be prepared through one
common method.
For example:
All alkenes can be prepared by dehydration of
relevant alcohols.
 Preparing ethene (Dehydration of ethanol)
C2H5OH → C2H4 + H2O
 Preparing propene (Dehydration of propanol)
C3H7OH → C3H6 + H2O

6. Members of the homologous series
have the same chemical properties.
For example:
All alkenes show addition reaction as added into
bromine.
 Addition of ethene with bromine
C2H4 + Br2 → C2H4 Br2
 Addition of propene with bromine
C3H6 + Br2 → C3H6 Br2

7. Alkane
Alkene
Alcohol
Carboxylic acid
Ester
Homologous Series