Why do atomic radii generally increase as you move down a group on the periodic table?

• A. Because the effective nuclear charge increases significantly, pulling electrons closer to the nucleus.
• B. Because the number of protons decreases, causing the atom to expand.
• C. Because additional electron shells are added, increasing the distance between the nucleus and the outermost electrons.
• D. Because atoms lose electrons as you move down a group, making them larger.

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 generally causes the atomic radius to increase.
4. Consider that although the nuclear charge (number of protons) increases down a group, the effect of increased shielding by inner electrons reduces the effective nuclear charge felt by the outermost electrons.
5. Conclude that the increased shielding and additional shells outweigh the increased nuclear charge, resulting in a larger atomic radius as you move down a group.