Here's why:

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

* Atoms are made up of even smaller particles: These are protons, neutrons, and electrons.

* Protons and neutrons are located in the atom's nucleus: They are held together by the strong nuclear force.

* Electrons orbit the nucleus: They are held in place by the electromagnetic force.

While atoms can be broken down into their constituent particles (protons, neutrons, and electrons), these smaller particles are not themselves considered "matter" in the same way that atoms are. They lack the properties we associate with matter, such as having mass and taking up space.

It's important to note that:

* Atoms can be broken down into even smaller particles: Protons and neutrons are made up of quarks, and there are other, more exotic particles that exist as well. However, these are not considered the "unbreakable" constituents of matter in the same way that atoms are.

* The concept of "unbreakable" is relative: In certain contexts, such as nuclear reactions, atoms can be broken apart, but in everyday life, they are considered stable and unbreakable.

So, while the concept of "unbreakable" is a bit fluid, atoms are the smallest units of matter that retain the chemical properties of an element and are considered the fundamental building blocks of everything around us.