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.
Definitions of an isotope: Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Another way to say the same thing is: Isotopes are atoms of the same element that have the same atomic number (whose symbol is Z) but different mass numbers (whose symbol is A).