What are protons and what are neutrons?

At the center of each atom is a nucleus containing protons and neutrons. All atoms of the same element have the same number of protons. This number is used to order the elements on the periodic table, starting with hydrogen, which has only one proton. Electrons are contained in shells around the nucleus. The total number of electrons always coincides with the number of protons in the nucleus. The proton and electron are electrically charged, but the neutron is not. Protons and neutrons are closely related in the nucleus of an atom, and electrons are distributed around the nucleus.