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

• A. Atomic radius remains constant.
• B. Atomic radius first increases, then decreases.
• C. Atomic radius increases.
• D. Atomic radius decreases.

Answer: (D)

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 from left to right across a period in the periodic table, the number of protons in the nucleus increases, which increases the nuclear charge.
3. Recognize that although electrons are added to the same principal energy level (same shell), the increasing positive charge in the nucleus pulls the electron cloud closer, reducing the atomic radius.
4. Note that the shielding effect remains relatively constant across a period because electrons are added to the same energy level, so inner electron shielding does not significantly increase.
5. Conclude that due to the stronger effective nuclear charge pulling electrons closer, the atomic radius decreases as you move from left to right across a period.