Which of the following best describes the trend in atomic radius as you move across a period from left to right on the periodic table?

• A. Atomic radius decreases due to increased nuclear charge pulling electrons closer.
• B. Atomic radius increases because more electron shells are added.
• C. Atomic radius remains constant because the number of protons and electrons increase equally.
• D. Atomic radius first increases, then decreases across the period.

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 cloud.
2. Recall that as you move across a period from left to right on the periodic table, electrons are added to the same principal energy level (same shell), so no new electron shells are added.
3. Recognize that the number of protons in the nucleus increases across a period, which increases the nuclear charge (positive charge attracting electrons).
4. Because the added electrons are in the same shell and the nuclear charge increases, the electrons are pulled closer to the nucleus, causing the atomic radius to decrease.
5. Therefore, the trend across a period is a decrease in atomic radius due to the increasing nuclear charge pulling electrons closer, despite the addition of electrons.