Which of the following best describes how ionic radii change as you move down a group in the periodic table?

• A. Ionic radii first increase and then decrease down a group.
• B. Ionic radii increase due to the addition of electron shells.
• C. Ionic radii decrease because nuclear charge increases.
• D. Ionic radii remain constant down a group.

Answer: (B)

Verified step by step guidance

1. Understand that ionic radius refers to the size of an ion, which depends on the number of electron shells and the effective nuclear charge experienced by the electrons.
2. Recall 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. Recognize that adding more electron shells increases the distance between the nucleus and the outermost electrons, which generally causes the ionic radius to increase.
4. Consider that although nuclear charge increases down a group, the effect of added electron shells (increased shielding) outweighs the increased nuclear charge, so the ionic radius does not decrease.
5. Conclude that the best description is that ionic radii increase down a group due to the addition of electron shells.