What is the difference between a compound and a molecule?
A compound is a substance that is composed from two or more different elements. Water (H2O), table salt (NaCl), carbon dioxide (CO2), methane (CH4) and chlorophyll (C55H72O5N4Mg) are a few examples of compounds. They are compounds because they each contain more than one kind of element. Things like nitrogen gas (N2) and buckminsterfullerene (C60) are not compounds since they only contains one kind of element (nitrogen gas contains only nitrogen and buckminsterfullerene contains only carbon).
Whether something is a molecule or not depends on the type of bond that is formed when its atoms join together. In general, electrons can be shared between atoms (a molecular bond) or electrons can be completely removed from one atom and given to another (an ionic bond). Molecules have molecular bonds.
Nitrogen gas (N2) is a molecule because the bond between the nitrogen atoms is a molecular bond. Water (H2O) is a molecular compound because it is a substance made from more than one kind of element that is held together with molecular bonds. Salt (NaCl) is an ionic compound because it is a substance made from more than one kind of element that is held together with ionic bonds.