Isotopes are different variables (or blends) of a certain element. Each blend has a different number of neutrons or protons (mass number), making it similar in composition, but definitely unique. Each isotope is identified by the particular chemical symbol of that element, followed by the mass number to differentiate it from all others. Isotopes are commonly observed in radioactive elements.
Isobars, on the other hand, are several different atoms, each a different chemical element, all having the same total number of protons and neutrons (nucleons). But, within the nucleons, there are varying numbers of protons and neutrons. The biggest difference between it and an isotope is the atomic number (amount of protons), not the mass number. For instance, Cl (chlorine) and Ar (argon) both have 40 nucleons, but the ratio of protons to neutrons is different.
Remember, each element is unique from all others! But, it's interesting to note how diversified, flexible, and similar the elements can be.