How are isotopes different from isobars? I keep swapping them up?

Both terms describe atoms, but they compare different things. Isotopes are atoms of the same element with the same number of protons (same atomic number Z) but different numbers of neutrons, so different mass numbers. Example: carbon-12 and carbon-14 are both carbon (6 protons) but have different masses. Isobars are atoms of different elements that happen to have the same mass number A but different atomic numbers. Example: argon-40 and calcium-40 both have mass number 40 but are different elements. A memory trick: in isoTOPes the 'p' reminds you the Proton number is the same; in isoBARs the mass (think 'A' for mass number) is the same while the elements differ. Compare Z for isotopes and A for isobars and you won't swap them.