Atoms can be classified by comparing their numbers of protons (atomic number, Z), neutrons (N), and total nucleons (mass number, A = Z + N). Several special terms describe atoms that share one of these quantities while differing in the others, and understanding the distinctions between them is important in nuclear chemistry and physics.

Isobars are atoms of different elements that have the same mass number (A) — i.e., the same total number of nucleons (protons + neutrons) — but different atomic numbers (Z), and therefore also different numbers of neutrons. Because their atomic numbers differ, isobars belong to different elements entirely, even though their overall nucleon count (and hence approximate atomic mass) is the same.

Example: ¹⁴C (carbon-14: Z = 6 protons, N = 8 neutrons, A = 14) and ¹⁴N (nitrogen-14: Z = 7 protons, N = 7 neutrons, A = 14) are isobars — both have a mass number of 14, but they are chemically distinct elements (carbon and nitrogen) because their proton counts differ. Another classic example is ⁴⁰Ar, ⁴⁰K, and ⁴⁰Ca, all sharing mass number 40 but being different elements.

Distinguishing the related terms clearly:

Since the question describes atoms with the same number of nucleons (same mass number) but different atomic numbers, this precisely matches the definition of isobars, and not isotopes (same Z), isotones (same N), or isoelectronic particles (same electron count, which is a separate criterion unrelated to nucleon count).