Which of the following best describes how the atomic size of atoms changes across a period in the periodic table?

• A. It first increases, then decreases.
• B. It remains constant across the period.
• C. It decreases from left to right.
• D. It increases from left to right.

Answer: (C)

Verified step by step guidance

1. Understand that atomic size (atomic radius) refers to the distance from the nucleus to the outermost electron in an atom.
2. Recall that as you move across a period from left to right, the number of protons in the nucleus increases, which increases the nuclear charge.
3. Recognize that the increased nuclear charge pulls the electrons closer to the nucleus, reducing the atomic radius.
4. Note that the electrons are added to the same principal energy level (same shell), so the shielding effect remains relatively constant and does not offset the increased nuclear charge.
5. Conclude that because of the stronger attraction between the nucleus and electrons, the atomic size decreases from left to right across a period.