Homo Atomic Molecules : These are the molecules which are made up of atoms of the same element. Most of the elementary gases consist of homo atomic molecules. For example hydrogen
gas consists of two atoms of hydrogen (H2). Similarly, oxygen gas consists of two atoms of oxygen (O2). In accordance with the number of atoms present in these molecules, they are classified as monoatomic, diatomic, triatomic or polyatomic molecules showing that they contain one, two, three or more than three atoms respectively.
For any homo atomic molecule, atomicity can be deduced using the formula:
Atomicity = (Molecular Mass)/(Atomic Mass )
Hetero Atomic Molecules : The hetero atomic molecules are made up of atoms of different elements. They are also classified as diatomic, triatomic, or polyatomic molecules depending upon the number of atoms present. H2O, NH3, CH4, etc. are the examples for hetero atomic molecules.