Why does atomic radius decrease as you move from left to right across a period in the periodic table?

• A. Because the atoms gain more neutrons, which decreases the size of the nucleus.
• B. Because additional electron shells are added, increasing the distance between the nucleus and the outer electrons.
• C. Because the number of protons increases, leading to a greater effective nuclear charge that pulls electrons closer to the nucleus.
• D. Because electrons are lost from the atom, reducing the size of the electron cloud.

Answer: (C)

Verified step by step guidance

1. Understand that atomic radius refers to the size of an atom, typically measured from the nucleus to the outer boundary of the electron cloud.
2. Recognize that as you move from left to right across a period, the number of protons in the nucleus increases, which increases the positive charge of the nucleus.
3. Know that electrons are added to the same principal energy level (same shell) across a period, so the distance of the outer electrons from the nucleus does not increase significantly.
4. Realize that the increased positive charge from more protons pulls the electrons closer to the nucleus, increasing the effective nuclear charge (Z_eff).
5. Conclude that this stronger attraction between the nucleus and electrons causes the atomic radius to decrease across a period, despite the addition of more electrons.