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.
1 Isotopes have the same atomic number (same number of protons), but a different atomic mass number (a different number of neutrons). 2  Isotopes behave the same chemically, because they are the same element. 3  The only difference is that one is heavier than the other, because of the additional neutrons.