In an investigation of periodic trends, a chemistry student compares the atomic radii of four neutral elements located in the third period: 11Na, 13Al, 15P, and 17Cl. Although each element has valence electrons occupying the third principal energy level, their atomic radii decrease systematically from sodium to chlorine. Which statement correctly explains this observed trend?
- A) Chlorine has the largest atomic radius because having seven valence electrons causes the greatest inter-electronic repulsion, expanding the electron cloud.
- B) Phosphorus has a larger atomic radius than aluminum because adding protons across the period increases the shielding effect of the core electrons.
- C) Sodium has the smallest atomic radius because its single valence electron experiences the weakest nuclear attraction, causing the orbital to collapse.
- D) Sodium has the largest atomic radius because having the lowest nuclear charge in this series yields the smallest effective nuclear charge, resulting in the weakest inward attraction on the valence shell.
