Welcome to the Community College of the Air Force (CCAF). Our college is a federally-chartered degree-granting institution that serves the United States Air Force's enlisted total force.
Isotopes of an element have nuclei with the same number of protons (the same atomic number) but different numbers of neutrons. Therefore, isotopes have different mass numbers, which give the total number of nucleons-the number of protons plus neutrons.
Isotopes are identified by their mass, which is the total number of protons and neutrons. There are two ways that isotopes are generally written. They both use the mass of the atom where mass = (number of protons) + (number of neutrons). Hydrogen is the only element where the isotopes are given specific names.