Complete the following sentences. Choose from the terms electron, electrons, proton, protons, neutron, neutrons. 1) Compared to the mass of a or a neutron, the mass of the is much smaller II) The identity of an element is determined by the number of its III) Isotopes differ in the number of IV) Protons and are located in the nucleus of the atom V) are negatively charged, are positively charged, and are neutral