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.
Individual isotopes have half-lives, not elements. Elements have many possible isotopes; the isotopes found in nature are stable or very long-lived. All elements from 1 to 82 have stable isotopes with two exceptions, technetium and promethium.