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

• A. Atoms gain more neutrons, which push the electrons farther from the nucleus.
• B. Electrons are removed from the atom, causing the remaining electrons to occupy larger orbitals.
• C. The number of protons decreases, reducing the nuclear charge and allowing electrons to spread out.
• 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 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 generally causes the atomic radius to increase.
4. Consider that although the number of protons (nuclear charge) also increases down a group, the effect of added electron shells outweighs the increased attraction, due to shielding by inner electrons.
5. Conclude that the primary reason atomic radius increases down a group is the addition of electron shells, which increases the size of the electron cloud and thus the atomic radius.