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

• A. Because atoms lose electrons as you move across a period, making them smaller.
• B. Because the number of protons increases, resulting in a greater effective nuclear charge that pulls electrons closer to the nucleus.
• C. Because additional electron shells are added, increasing the distance between the nucleus and the outer electrons.
• D. Because the shielding effect increases significantly, causing electrons to be held less tightly.

Answer: (B)

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 because the effective nuclear charge (Z_eff) increases.
5. Understand that the shielding effect remains relatively constant across a period since electrons are added to the same shell, so it does not offset the increased nuclear charge, resulting in a smaller atomic radius.