Which of the following best explains why the atomic radius increases as you move from the top to the bottom of a group in the periodic table?

• A. Additional electron shells are added, increasing the distance between the nucleus and the outermost electrons.
• B. Electrons are removed from the atom, causing the atom to expand.
• C. Atoms gain more neutrons, which increases the size of the electron cloud.
• D. The number of protons decreases, reducing the nuclear charge and allowing electrons to spread out.

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. Recall 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 that although the nuclear charge (number of protons) increases down a group, the effect of added inner electron shells (shielding) reduces the effective nuclear attraction on the outermost electrons.
5. Conclude that the primary reason for the increase in atomic radius down a group is the addition of electron shells, which outweighs the increased nuclear charge and results in a larger atomic size.