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

• A. Atoms lose electrons as you move down a group, resulting in a larger radius.
• B. The number of protons decreases, causing the atom to expand.
• C. Effective nuclear charge increases significantly, pulling electrons closer to the nucleus.
• D. 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 causes the atomic radius to increase.
4. Consider the concept of effective nuclear charge (Z_eff), which is the net positive charge experienced by electrons; although it increases slightly down a group, the effect of added shells dominates.
5. Conclude that the primary reason atomic radius increases down a group is due to the addition of electron shells, which outweighs the pull of the nucleus on the outer electrons.