Here's why:

* Fundamental Building Block: Atoms are the smallest unit of an element that retains the chemical properties of that element. They are the foundation for all other matter.

* Subatomic Particles: Atoms are composed of even smaller particles called protons, neutrons, and electrons. These particles interact to determine an atom's behavior.

* Basic Structure: Atoms are incredibly small and have a simple structure: a dense nucleus containing protons and neutrons, surrounded by a cloud of electrons.

While atoms are incredibly small and complex in their own right, they are the most basic and fundamental unit of matter.