Here's the breakdown:

* Atom: The basic unit of a chemical element. It's the smallest unit of matter that retains the chemical properties of that element. Examples: hydrogen atom, oxygen atom, carbon atom.

* Molecule: A group of two or more atoms held together by chemical bonds. Examples: water molecule (H₂O), carbon dioxide molecule (CO₂), oxygen molecule (O₂).

Think of it like this: Legos are like atoms. You can build various structures (like houses, cars, etc.) with them. These structures are like molecules.

So, a single atom cannot be made of molecules, just like a single Lego block cannot be made of a house.