Which of the following best explains why atomic radius increases as you move down a group in the periodic table?

• A. The effective nuclear charge increases, pulling electrons closer to the nucleus.
• B. Electrons are removed from the outer shell, decreasing electron-electron repulsion.
• C. Additional electron shells are added, increasing the distance between the nucleus and the outermost electrons.
• D. Atoms gain more protons, which decreases the atomic radius.

Answer: (C)

Verified step by step guidance

1. Understand that atomic radius refers to the average distance from the nucleus to the outermost electrons in an atom.
2. Recognize that as you move down a group in the periodic table, each successive element has an additional electron shell compared to the one above it.
3. Know that adding more electron shells increases the distance between the nucleus and the outermost electrons, which tends to increase the atomic radius.
4. Consider that although the number of protons (and thus the nuclear charge) increases down a group, the effect of increased distance and electron shielding from inner shells reduces the effective nuclear attraction on the outer electrons.
5. Conclude that the primary reason atomic radius increases down a group is the addition of electron shells, which outweighs the increase in nuclear charge and results in a larger atomic size.