Which statement explains why atomic radius decreases across Period 3 from sodium to chlorine?
Answer and explanation
Correct answer: D. The nuclear charge increases while the shielding stays about the same
- Step 1: Across a period, electrons are added to the same shell while protons are added to the nucleus.
- Step 2: The greater nuclear charge pulls the electrons in more strongly, so the radius falls.
Answer
The nuclear charge increases while the shielding stays about the same.
Why not the others: The number of electron shells increases across the period: the number of shells is the same across a period. The number of neutrons decreases across the period: neutrons do not decrease and have no effect on radius. The outer electrons become more shielded across the period: shielding stays about the same across a period.
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