Homologous Series

Definition

Homologous series is a group of compounds with the same general formula, have similar chemical properties because they have same functional group and show a gradation in physical properties as a result of increase in size and molecular mass of molecules. #ChemistryDefinitions

Definition

Functional group is an atom or group of atoms that gives a molecule of an organic compound its characteristics chemical properties i.e. chemical reactions.

Note

functional group also contributes to its characteristic physical properties of organic compounds.

Alkanes

Functional Group	Example
Alkanes do not have any functional groups. There are only C-C and C-H bonds

Alkenes

Functional Group	Example
carbon-carbon double bond

Alcohols

Functional Group	Example
hydroxyl group

Carboxylic Acids

Functional Group	Example
carboxyl group

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General Characteristics of Homologous Series

organic compounds in the same homologous series have following characteristics:

• members of the same homologous series has the same general formula.
• they have same functional group, thus (next point)
• they have similar chemical properties
• each member of the series differs from the next by an additional $-C{H}_2-$ unit hence a change of 14 units in its molecular mass.
• there is a gradual change in their physical properties as we go down the series from one member to the next, due to an increase in its molecular mass. (melting point, boiling point, and viscosity)

for e.g. the boiling points and viscosity of members increase down the homologous series.

• covered here:

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Naming Organic Compounds

Name of organic compound is divided into 2 parts:

• prefix tells us number of carbon atoms in each molecule
• suffix tells us which homologous series the compound belongs to.

Prefix	Number of Carbon atoms
meth-	1
eth-	2
prop-	3
but-	4

Suffix	Homologous Series
-ane	alkane
-ene	alkene
-ol	alcohol
-oic acid	carboxylic acid

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