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

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

Answer: (A)

Verified step by step guidance

1. Understand that atomic radius refers to the size of an atom, typically measured as the distance from the nucleus to the outermost electron shell.
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 valence electrons after accounting for shielding by inner electrons; while Z_eff does increase 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 modest increase in nuclear charge, causing the outer electrons to be farther from the nucleus.