<human>:  What is the difference between a molecule and an atom?
<bot>: The main difference between a molecule and an atom is that molecules are composed of two or more atoms held together by a chemical bond, while atoms are the basic building blocks of all matter and cannot be broken down further without changing the identity of the substance they form. Atoms are composed of protons, neutrons, and electrons, but molecules are composed of a combination of different atoms held together by chemical bonds.