Nuclear vocabulary: atoms of different elements having the same value of (mass number − atomic number) are called what?

Introduction / Context:
Several “iso-” terms distinguish nuclear relationships: isotopes, isobars, isotones, and nuclear isomers. Knowing which quantity remains the same in each category is a common exam check that prevents confusion when analyzing decay chains and nuclear reactions.

Given Data / Assumptions:

• Mass number A = protons + neutrons.
• Atomic number Z = number of protons.
• A − Z = number of neutrons N.

Concept / Approach:
If two or more atoms have the same value of A − Z, they have the same neutron count N, regardless of Z. The term for nuclides with equal neutron numbers is “isotones.” In contrast, isotopes share Z, isobars share A, and isomers share A and Z but differ in nuclear energy (metastable states).

Step-by-Step Solution:
Translate the condition “same (A − Z)” to “same N.”Recall definitions: isotopes (same Z), isobars (same A), isotones (same N), isomers (same A and Z but excited state).Pick “Isotones.”

Verification / Alternative check:
Example: 14C (Z=6, N=8) and 15N (Z=7, N=8) are isotones because both have eight neutrons though A and Z differ.

Why Other Options Are Wrong:

• Isomers: same A and Z, different nuclear energy states.
• Isotopes: same Z but different N (not fixed A − Z).
• Isobars: same A, not same A − Z.
• Isoelectronic: same electrons for ions/molecules; atomic electrons, not nuclear.

Common Pitfalls:
Confusing “isobars” (A same) with “isotones” (N same); overlooking that A − Z equals neutron count.

Final Answer:
Isotones