An atom is the smallest particle of an element. It may or may not have independent existence. A molecule is the smallest particle of a substance which is capable of independent existence.
The word atom comes from Greek word 'Atomos' meaning indivisible . An atom is a basic building block for all matter in the universe.It is like if you want a language,you need alphabets. Atoms are extremely small and are made up of a few even smaller particles. All atoms are made up of a number of electrons, protons and neutrons.
Inside an Atom:
The protons are located in the center (which is known as nucleus) of an atom, each atom has at least one proton. The neutrons also are located in the nucleus of the atom. The electrons are very small particles located outside the nucleus.
Atoms fit together with other atoms to make up matter. It takes a lot of atoms to make up anything. There are different kinds of atoms based on the number of electrons, protons, and neutrons each atom contains. Different substances have different types of atoms. Each different kind of atom makes up an element.
Any time two atoms join together, they make a molecule. All the stuff around you is made up of molecules. This includes you! You are actually made up of trillions and trillions of different types of molecules.
The atoms of certain elements readily bond with other atoms to form molecules. Examples of such elements are oxygen and chlorine.