As you move from left to right across a period in the periodic table, what happens to the atomic radius of the elements?

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

Answer: (D)

Verified step by step guidance

1. Understand that the atomic radius is the average distance from the nucleus to the outermost electrons in an atom.
2. Recognize 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 positive charge (nuclear charge).
3. Note that electrons are added to the same principal energy level (same shell) across a period, so the shielding effect remains relatively constant.
4. Because the nuclear charge increases while shielding remains constant, the effective nuclear charge felt by the outer electrons increases, pulling the electrons closer to the nucleus.
5. Conclude that this increased attraction causes the atomic radius to decrease as you move from left to right across a period.