Nucleus at the centre of an atom contains two types of particle, protons (positive charge) and neutrons (no charge). Electrons are negatively charged particles that move around the nucleus. An atom has no overall charge because the number of electrons is equal to the number of protons and their charges are equal and opposite.
All atoms of an element contain the same number of protons. Elements are arranged in order of their atomic numbers (number of protons) in the periodic table.