What are atoms made of?

Atoms are such particles of matter of a very microscopic size and mass. The nucleus and electrons are the constituent parts of atoms. If the number of electrons in the nucleus coincides with the number of protons, then this nucleus is electrically neutral. If on the contrary, then such an atom is called an ion. The nucleus, which carries more than 99.9% of the mass of an atom, is linked by a strong interaction and consists of positively charged protons and uncharged neutrons. Atoms are classified according to the number of protons and neutrons in the nucleus.