Atoms are made of sub-atomic particles called electrons, protons and neutrons.Protons and neutrons are found in the nucleus and are called nucleons. Protons are positively charged and neutrons have no charge.Electrons are negatively charged and surround the nucleusThe strong nuclear force holds protons and neutrons together in the nucleus. The strong nuclear force acts only over short distances and overcomes the electrostatic repulsion between the protons.Electrons orbit the nucleus in shells.