Isotopes are any of the different forms of an element each having different atomic mass (mass number). 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. A nuclide is any particular atomic nucleus with a specific atomic number Z and mass number A; it's equivalently an atomic nucleus with a… (More on Isotope)