The charge on an electron is -1. The atomic number is the number of protons an atom has. It is characteristic and unique for each element. Isotopes can be used to determine the diet of ancient peoples by determining proportions of isotopes in mummified or fossilized human tissues. Biochemical pathways can be deciphered by using isotopic tracers.
Isotopes are also the source of radiation used in medical diagnostic and treatment procedures.
Note that each of these isotopes of hydrogen has only one proton. Isotopes differ from each other in the number of neutrons, not in the number of protons. Image from W.H. Freeman and Sinauer Associates, used by permission. Some isotopes are radioisotopes, which spontaneously decay, releasing radioactivity . Other isotopes are stable.