Here's why:

* Molecules are formed when two or more atoms bond together.

* Atoms are the fundamental building blocks of all matter. They are the smallest unit of an element that retains the chemical properties of that element.

Think of it like this:

* A molecule is like a Lego structure made of many individual pieces.

* The individual Lego pieces are like atoms. You can't break a Lego piece down any further and still have a Lego piece. Similarly, you can't break an atom down any further and still have that same element.