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

• A. Because the number of protons decreases, reducing the nuclear charge.
• B. Because the atoms gain more neutrons, which expand the electron cloud.
• C. Because electrons are removed from the atom, making it larger.
• 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 (energy level) compared to the one above it.
3. Know that adding more electron shells increases the distance between the nucleus and the outermost electrons, which naturally increases the atomic radius.
4. Consider the effect of shielding: inner electron shells partially block the attraction between the nucleus and the outer electrons, allowing the outer electrons to be held less tightly and thus spread out more.
5. Conclude that the increase in atomic radius down a group is primarily due to the addition of electron shells and the resulting increase in electron shielding, not because of changes in proton number or neutron count.