Why does the atomic radius increase as you move down a group in the periodic table?

• A. Because the effective nuclear charge increases, pulling electrons closer to the nucleus.
• B. Because electrons are removed from the outer shell, making the atom larger.
• C. Because atoms gain more protons, which decreases the size of the atom.
• D. Because additional electron shells are added, increasing the distance between the nucleus and the outermost electrons.

Answer: (D)

Verified step by step guidance

1. Understand that atomic radius refers to the size of an atom, typically measured from the nucleus to the outer boundary of the electron cloud.
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 leads to a larger atomic radius.
4. Consider the concept of effective nuclear charge (Z_eff), which is the net positive charge experienced by outer electrons; although Z_eff increases slightly down a group, the effect of added shells dominates.
5. Conclude that the increase in atomic radius down a group is primarily due to the addition of electron shells, which outweighs the pull of the nucleus on the outer electrons.