Which trend is observed in the atomic radii of main-group elements as you move from left to right across a period in the periodic table?

• A. Atomic radius first increases, then decreases
• B. Atomic radius remains constant
• 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 the increased nuclear charge pulls the electrons closer to the nucleus because the electrons are attracted more strongly, reducing the size of the electron cloud.
4. Note that although electrons are added as you move across a period, they are added to the same principal energy level, so the shielding effect does not increase significantly to counteract the increased nuclear charge.
5. Conclude that due to the stronger attraction between the nucleus and electrons, the atomic radius decreases from left to right across a period.