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

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

Answer: (B)

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. Recognize that as you move from left to right across a period, electrons are added to the same principal energy level (same shell), so the number of electron shells does not increase.
3. Note that the number of protons in the nucleus increases by one for each successive element, increasing the positive charge of the nucleus.
4. Realize that this increased positive charge (nuclear charge) pulls the electrons closer to the nucleus because the electrons experience a stronger electrostatic attraction.
5. Understand that although electrons are added, the shielding effect (repulsion by inner electrons) does not increase significantly within the same shell, so it does not offset the increased nuclear charge, resulting in a decrease in atomic radius.