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.

* Elements are pure substances made up of only one type of atom. For example, gold is made up of only gold atoms.

* You can't break down an atom into anything smaller and still have the same element. If you try to break an atom apart, you get different things (like protons, neutrons, and electrons), but those aren't the same element anymore.

Let me know if you'd like to know more about atoms!