The smallest unit of matter that retains all of an element’s chemical properties is an atom. The fundamental unit of all matter is the atom. The atom of each element, in other words, is distinct from the atom of every other element. Even an atom will however be divided into smaller parts, called quarks.
An atom, with the same chemical properties as the bulk element, is the smallest particle in an element. Dalton’s Atomic Theory was the first accurate theory which explained the existence of matter.
All matter is composed of extremely small particles in the Universe. They are in continuous motion and with each other in constant contact. Atoms form elementary particles and molecules form atoms. In the universe, there is a finite number of kinds of atoms that are the elements of the periodic table.