Here's why:

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

* Molecules are formed when two or more atoms bond together chemically. These bonds can be covalent (sharing electrons) or ionic (transferring electrons).

For example, a water molecule (H₂O) is made of two hydrogen atoms and one oxygen atom joined together.

Let me know if you'd like more examples!