Atomic Structure – Atoms of one element differ from atoms of all other elements primarily in which characteristics?

Introduction / Context:
Each chemical element is uniquely identified by its atomic number (Z), which equals the number of protons in the nucleus. This determines the number of electrons in a neutral atom and thus drives its electronic configuration and chemical properties.

Given Data / Assumptions:

• We compare features that could distinguish one element from another.
• Atomic number (Z) uniquely defines the element’s identity.
• Electronic configuration shapes chemical behavior for the neutral atom.

Concept / Approach:
Different elements must have different atomic numbers. Consequently, their full electronic configurations also differ for neutral atoms (though elements in the same group may share valence patterns). Neutron count can vary within the same element (isotopes), so it does not uniquely distinguish elements.

Step-by-Step Solution:
Identify the invariant: atomic number is unique to each element.Link atomic number to electron count in neutral atoms, which sets electronic configuration.Eliminate choices that rely on neutron number or only valence electrons.Choose “atomic number and electronic configuration”.

Verification / Alternative check:
Elements in the same group (e.g., alkali metals) share valence electron counts but still have different complete configurations and different atomic numbers. Isotopes show the same Z with different neutron numbers, confirming neutrons are not decisive for element identity.

Why Other Options Are Wrong:

• number of neutrons and number of valence electrons: neutron number is not unique to different elements; valence electron counts can repeat across groups.
• atomic number and number of valence electrons: valence counts can be identical for several elements.
• number of neutrons and electronic configuration: neutron number varies within an element; configuration is derivative of Z.

Common Pitfalls:
Confusing isotopes (same element, different neutron counts) with different elements. Only atomic number fixes the elemental identity.

Final Answer:
atomic number and electronic configuration