The protons and the neutrons are found in the nucleus. Both protons and neutrons have mass. Protons are positively charged. Neutrons are neutral. Electrons are so small that they have relatively little mass.
Electrons carry a negative charge.
Atoms are mostly empty space. Each element has its own characteristic atomic number. The elements are arranged in the Periodic Table by atomic number. Periodicity of properties is a result of the distribution of electrons. The total mass of the atom comes from the atom s protons and neutrons.