Here's why:

* Compound: A substance formed when two or more different elements are chemically bonded together.

* Molecule: The smallest unit of a compound that retains the chemical properties of that compound.

For example, water (H₂O) is a compound made up of hydrogen and oxygen. The smallest unit of water that still exhibits the properties of water is a water molecule, which consists of two hydrogen atoms bonded to one oxygen atom.

Let me know if you have any other questions!