Chemistry fundamentals — What are atoms of the same chemical element that have different masses called? (Note: These atoms have the same atomic number but different mass numbers due to a different number of neutrons.)

Introduction:
In introductory general chemistry and nuclear chemistry, it is essential to distinguish among related terms that describe nuclides. This question targets the definition of atoms of the same element that differ in mass because of different neutron counts.

Given Data / Assumptions:

• All atoms considered belong to the same element (same atomic number Z).
• Observed masses differ (different mass number A).
• Chemical behavior is largely similar; nuclear properties can differ.

Concept / Approach:
Isotopes are nuclides of the same element (same Z) but different mass numbers (A) due to varying numbers of neutrons. Because electrons govern chemistry, isotopes show nearly identical chemical properties, though physical properties (density, diffusion rates) and nuclear stability can vary.

Step-by-Step Solution:
Identify the defining feature: same Z (element identity), different A (mass).Recall terminology: isotopes → same Z; isobars → same A; isotones → same N (neutrons).Match the definition to the term “isotopes.”

Verification / Alternative check:
Examples include ¹²C, ¹³C, and ¹⁴C for carbon; ¹H, ²H (deuterium), and ³H (tritium) for hydrogen.

Why Other Options Are Wrong:

• Isobars: same mass number but different elements (different Z).
• Isotones: same neutron number N but different Z.
• Allotropes: different structural forms of the same element in the same physical state (applies to solids like carbon, not individual atoms).
• “None of these” is incorrect because a standard term exists: isotopes.

Common Pitfalls:
Confusing isobars and isotopes; thinking allotropes refer to atomic differences rather than structural forms of elements.

Final Answer:
Isotopes