The atom is the smallest unit of matter. By definition, an atom is the smallest indivisible unit of matter with characteristic properties of an element. Atoms are so extremely tiny that a typical atom is about 100 picometers in size.
Generally, atoms consist of a nucleus and an electron cloud. This nucleus includes positively charged protons and neutral neutrons. While the negatively charged electrons are located in the electron cloud. The number of protons in a stable atom is equal to the number of electrons. When this number isn’t balanced, it forms a charge thereby making it an ion.