Isotopes are variants of a particular chemical element. While all isotopes of a given element share the same number of protons, each isotope differs from the others in its number of neutrons. There are stable and radioactive isotopes. Chemical elements, as a rule, are a mixture of isotopes- atoms with identical serial numbers (charges), but different mass numbers. The greatest number of isotopes has a tin (Z = 50) with xenon (Z = 54), nine isotopes, cadmium (Z = 48) and tellurium (Z = 52) each have eight isotopes, other elements have a smaller number of isotopes. There are elements that have only one stable isotope, and they are simple. There are F, Na, P, V, Mn, Au, Be,Al.