The concept of an indivisible atom was initially proposed by the ancient Greek philosopher Democritus around 400 BCE. He suggested that matter is composed of tiny, indivisible particles called "atoms," which means "uncuttable" in Greek. However, our understanding of atoms has evolved significantly since then.
In modern physics, we have discovered that atoms are made up of smaller subatomic particles. The three main subatomic particles are protons, neutrons, and electrons. Protons and neutrons are composed of even smaller particles called quarks. Quarks are elementary particles and are considered to be the fundamental building blocks of matter. There are six known types or flavors of quarks: up, down, charm, strange, top, and bottom.
While quarks are indeed smaller than atoms, it is important to note that they are not found in isolation. Quarks are always found bound together in groups of two or three, forming composite particles called hadrons, which include protons and neutrons. The strong force, one of the fundamental forces of nature, binds quarks together within these composite particles. This strong force becomes stronger as quarks move apart, making it impossible to separate individual quarks from a hadron.
In the case of an atom, the nucleus, which contains protons and neutrons, is surrounded by a cloud of electrons. The electrons are not made up of quarks but are considered elementary particles. The nucleus and the electrons are held together by the electromagnetic force.
So, while atoms are not truly indivisible, we cannot break them apart into quarks without disrupting the delicate balance of forces that hold them together. The concept of an indivisible atom is a simplified model that serves as a useful framework for understanding the behavior of matter at a macroscopic level.