Molecules can be classified in several ways: 1) Based on the number of atoms - monoatomic (one atom), diatomic (two atoms), or polyatomic (more than two atoms). 2) Based on the type of atoms - homonuclear (same type of atoms) or heteronuclear (different types of atoms). 3) Based on size - micro molecules are small with low molecular weights, while macro molecules are very large with high molecular weights, such as haemoglobin.

1. MOLECULE

2. DEFINITION
When any two or more atoms form chemical bonds, they form
a molecule.

3. TYPES OF MOLECULES
The molecules can be divided into many
types on the following
a)On the basis of atomicity
b)On the basis of kind of atoms
c)On the basis of size of molecules

4. On the basis of atomicity
• The number of atoms in a molecule determines in atomicity.
• On the basis of atomicity molecules may be of following types
• MONOATOMIC MOLECULES:
• “Those molecules which consist of only one atom are known as
monoatomic molecule”
• Example: He,Ne, Ar etc.
He
Ne
Ar

5. • DIATOMIC MOLECULES:
• “Those molecules which consist of two atoms are known as diatomic
molecule”
• Example: H2, O2, HCl, N2 etc.
POLYATOMIC MOLECULES:
“Those molecules which consist of more than two atoms are known as
diatomic molecule”
Example: O3,P4,CH4, H2SO4,C6H12O6 etc.
O O
C
H
H
H
H

6. On the basis of kind of atoms:
• On the basis of kind of atoms, the molecules are of following types.
• HOMONULEAR MOLECULES:
• “ Those molecules which consist of only one kind of atoms are known as
homonuclear molecules”
• EXAMPLES: He,Cl2,O3,P4,S8 etc.
• HETERONULEAR MOLECULES:
• “ Those molecules which consist of different kind of atoms are known as
heteronuclear molecules”
EXAMPLES: HCl, NH3,H2SO4, C6H12O6

7. • The sizes of molecules are definitely bigger than atoms. The sizes of
molecules depend upon the number of atoms present in them and their
shapes. On the basis of size, molecules are of following types.
• Micro molecules:
• “Those molecules which are very small and have low molecular weights
are known as micromecules.”
• The micro molecules contain relatively small number of atoms.
• Example: HCl, NH3, H2SO4, C6H12O6 etc.
On the basis of size of molecules:

8. • Macro molecules:
• “Those molecules which are very large size and have high molecular
weights are known as macro molecules.”
• Example: Haemoglobin is a macromolecule found in blood. It helps to
carry oxygen from our lungs to all parts of our body.