Atomic structure concept check: isotopes of the same chemical element share which identical property?

Introduction / Context:
Isotopes are variants of a chemical element that differ in the number of neutrons but possess the same number of protons. Because chemical behaviour arises from electron arrangement determined by nuclear charge (atomic number), isotopes of an element show the same ground-state electronic configuration in neutral atoms and therefore very similar chemistry.

Given Data / Assumptions:

• Isotopes: same atomic number Z, different neutron count N.
• Neutral atoms considered (no ionisation states) to discuss configuration cleanly.
• Chemical properties principally depend on electron configuration.

Concept / Approach:
The atomic number fixes the electron count of a neutral atom and thus its electronic configuration. Changing neutrons alters mass number (A = Z + N) and nuclear stability but not the electronic shell structure for the neutral atom. Consequently, isotopes have essentially identical valence structures and similar chemical reactions, with small kinetic isotope effects in some cases.

Step-by-Step Solution:
Define isotope: same Z, different N.Infer that A (mass number) changes with N.Recognise electronic configuration depends on Z for neutral atoms.Therefore, isotopes share electronic configuration.

Verification / Alternative check:
Consider chlorine-35 and chlorine-37: both have Z = 17, hence identical electron distribution (1s^2 2s^2 2p^6 3s^2 3p^5) and similar chemistry; only mass-dependent properties (diffusion rates, vibrational frequencies) vary slightly.

Why Other Options Are Wrong:

• Number of neutrons: By definition, different.
• Mass number: Different because N differs.
• Atomic weight: A weighted average over isotopic distribution; not the same for individual isotopes and certainly not identical across isotopes.
• Nuclear mass exactly equal: Mass differs with neutron count.

Common Pitfalls:
Confusing atomic weight (periodic table average) with mass number of a single isotope; forgetting that ions can alter electron counts—here we are comparing neutral atoms for configuration.

Final Answer:
Electronic configuration