Apentix/AP Chemistry/Unit 2: Molecular and Ionic Compound Structure and Properties/Question

AP Chemistrymediummcq1 pt

O²⁻, F⁻, Na⁺, and Mg²⁺ all contain 10 electrons. Which particle is largest, and why?

A.Mg²⁺, since losing electrons expands the remaining cloud

B.Na⁺, because sodium is the heaviest of the four elements

C.O²⁻, whose 8 protons barely restrain its 10 electrons

D.They are all identical in size because electron counts match

Explanation

Core Concept

Isoelectronic species differ only in nuclear charge, and radius shrinks as that charge rises. Oxygen's 8 protons hold 10 electrons loosely, so its cloud balloons outward. Fluorine with 9 protons, sodium with 11, and magnesium with 12 progressively compress the same electron count, giving radii in the order O²⁻ > F⁻ > Na⁺ > Mg²⁺.

Correct Answer

CO²⁻, whose 8 protons barely restrain its 10 electrons

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