Which of the following factors best explains why atomic radii generally increase when moving down a group in the periodic table?

• A. Atoms gain more protons, which strongly attract electrons and decrease atomic radius.
• B. The addition of electron shells increases the distance between the nucleus and the outermost electrons.
• C. Electrons are removed from the outer shell, causing the atom to expand.
• D. The effective nuclear charge experienced by valence electrons increases significantly down a group.

Answer: (B)

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 moving down a group in the periodic table means adding more electron shells (energy levels) to the atoms.
3. Recall that each additional electron shell increases the distance between the nucleus and the outermost electrons, which tends to increase the atomic radius.
4. Consider the effect of nuclear charge (number of protons): although it increases down a group, the added inner electron shells shield the outer electrons from this increased positive charge, reducing the effective nuclear attraction on the valence electrons.
5. Conclude that the dominant factor causing atomic radii to increase down a group is the addition of electron shells, which outweighs the effect of increased nuclear charge.