Isotopes are atoms of the same element with the same atomic number but different mass numbers. They have the same number of protons but a different number of neutrons.
Example: ¹H, ²H, and ³H are isotopes of hydrogen.

Isobars are atoms of different elements with the same mass number but different atomic numbers. They have the same total number of protons and neutrons, but arranged differently.
Example: ⁴⁰Ca and ⁴⁰Ar are isobars.