The difference between atom and molecule can be drawn clearly on the following grounds:
Atom is defined as the smallest unit of an element that may or may not exist independently. On the other hand, molecule implies the collection of atoms linked together by bonds, indicating the smallest unit of the compound.
Atoms may or may not exist in the free state, but molecules exist in the free state.
Atoms consist of a nucleus (containing protons and neutrons) and electrons. In contrast, a molecule consists of two or more identical or different atoms, chemically combined.
The shape of an atom is spherical while molecules can be linear, angular or rectangular.
Atoms are highly reactive, i.e. they participate in a chemical reaction without additional decomposition into subatomic units. However, this does not apply to noble gas atoms. In contrast, molecules are less reactive, as they do not participate in a chemical reaction.
Atoms possess a nuclear bond, as it entails an electrostatic attraction between the nucleus and the electron. In contrast, there exists a chemical bond between the atoms of a molecule, hence it consists of single, double or triple bonds.
