This statement can sound quite confusing at first, but it makes sense when we break down the definitions of compounds and molecules.
A molecule is formed when two or more atoms bond together. These atoms can be of the same type, such as two oxygen atoms bonded together to form O2, or they can be different types, like water (H2O), which consists of both hydrogen and oxygen atoms. Therefore, all compounds qualify as molecules because they involve multiple atoms bonded together.
On the other hand, not all molecules are compounds. A compound specifically refers to a substance that contains at least two different types of atoms. For example, O2, which is a molecule made up of two oxygen atoms, is not a compound because it only consists of one type of atom. In contrast, H2O is a compound because it contains both hydrogen and oxygen atoms.
In summary, while all compounds are indeed molecules (since they consist of bonded atoms), the reverse is not true because a molecule can also consist of identical atoms, which does not qualify it as a compound.