Nuclear terminology: atoms that contain the same number of neutrons but a different total number of nucleons (i.e., different Z and/or A) are called what?

Introduction / Context:Nuclear classification terms—such as isotopes, isobars, isotones, and isomers—appear frequently in chemistry and nuclear engineering exams. Each term captures a different way nuclides can be “the same” or “different” with respect to proton number, neutron number, or overall nucleon number. Knowing the exact definitions prevents common mix-ups when interpreting nuclear reaction equations or decay series.

Given Data / Assumptions:

• We compare nuclides by Z (protons), N (neutrons), and A (nucleons = Z + N).
• We assume ground-state identity unless otherwise specified (isomers differ by nuclear energy state).

Concept / Approach:Isotopes: same Z, different N (therefore different A).Isobars: same A, different Z (and thus different N).Isotones: same N, different Z (and usually different A).Isomers: same Z and A but different nuclear energy states (metastable vs. ground state). Given the stem—“same number of neutrons, but different number of nucleons”—we are clearly describing nuclides that share N yet do not share A, which is the hallmark of isotones.

Step-by-Step Solution:Translate the statement “same neutrons” → same N.“Different nucleons” → different A.Same N with different A implies different Z as well.By definition, such nuclides are isotones.

Verification / Alternative check:Examples: 14C (Z = 6, N = 8) and 15N (Z = 7, N = 8) are isotones (same N = 8), not isotopes or isobars. This aligns with the formal definitions used in nuclear data tables and textbooks.

Why Other Options Are Wrong:Isobars: same A, not applicable here.Isotopes: same Z, not “same N.”Isoters: not a standard nuclear classification term in this context.Isomers: same Z and A, differing by nuclear energy state; not governed by N sameness.

Common Pitfalls:Confusing “bar” (A same) with “tone” (N same).Assuming any two nuclides with the same mass number must be isotopes; they are isobars if Z differs.

Final Answer:Isotones