Isotopes and neutral atoms: for the neutral atoms of an element’s isotopes, which property differs among them?

Introduction / Context:
Isotopes are atoms of the same element with the same number of protons (same atomic number) but different numbers of neutrons. This leads to different masses while chemical identity, governed by proton count and electron configuration, remains the same for neutral atoms. Distinguishing which properties change or stay constant is essential in nuclear chemistry and analytical applications like mass spectrometry and radiochemistry.

Given Data / Assumptions:

• Isotopes share the same element identity Z (protons).
• Neutral atoms possess equal numbers of protons and electrons.
• We compare atomic weight (mass), atomic number, proton count, and electron count.

Concept / Approach:
Because isotopes differ in neutron number, their mass numbers and atomic weights differ. However, atomic number (Z) is identical for all isotopes of a given element, and neutral atoms have Z electrons to balance Z protons. Therefore, among listed properties, only atomic weight changes from isotope to isotope, while atomic number, number of protons, and number of electrons remain constant for neutral atoms of the same element.

Step-by-Step Solution:

Verification / Alternative check:
Periodic table listings often show weighted average atomic masses reflecting natural isotopic abundances, confirming that individual isotopes have distinct masses that contribute to the average value.

Why Other Options Are Wrong:

• Atomic number/number of protons: fixed for the element; changing these changes the element.
• Number of electrons (neutral atoms): equals Z for neutrality.
• Nuclear charge state: determined by Z, same across isotopes of the same element.

Common Pitfalls:
Confusing ionic charge (electron gain/loss) with isotopic differences; thinking isotopes alter chemical valence dramatically—most chemistry is similar despite mass differences.

Final Answer:
Atomic weights