Hetro atomic molecules must have more than one type of atom, such as water (H2O). 
A homoatomic molecule is a molecule consisting of atoms of the same element. examples are - oxygen (O2), hydrogen (H2), and nitrogen (N2). Homo atomic molecules are also called "Diatomic" molecules.
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The homo-atomic are the molecules with same types of atoms.
 Example: Hydrozen, surphur.
The hetero-atomic molecules are the molecules with different kinds of atoms. Example: water.
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