As the atomic number increases 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 increases.
• C. The atomic radius decreases.
• D. The atomic radius remains constant.

Answer: (C)

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 atomic number increases, meaning more protons are added to the nucleus.
3. Know that with each additional proton, the positive charge of the nucleus increases, which pulls the electrons closer to the nucleus due to stronger electrostatic attraction.
4. Note that although electrons are also added across the period, they enter the same principal energy level, so the shielding effect does not increase significantly to counteract the increased nuclear charge.
5. Conclude that because the effective nuclear charge increases without a significant increase in shielding, the atomic radius decreases as you move from left to right across a period.