Which of the following best describes how atomic radius changes within a group and across a period in the periodic table?

• A. Atomic radius increases both down a group and across a period from left to right.
• B. Atomic radius increases down a group and decreases across a period from left to right.
• C. Atomic radius decreases both down a group and across a period from left to right.
• D. Atomic radius decreases down a group and increases across a period from left to right.

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 moving down a group (column) in the periodic table adds electron shells, which increases the distance between the nucleus and the outermost electrons, causing the atomic radius to increase.
3. Know that moving across a period (row) from left to right adds protons to the nucleus and electrons to the same shell, increasing the effective nuclear charge, which pulls electrons closer to the nucleus and decreases the atomic radius.
4. Summarize the trend: atomic radius increases down a group due to added electron shells, and decreases across a period from left to right due to increasing nuclear charge without additional shielding.
5. Use this understanding to identify the correct description: 'Atomic radius increases down a group and decreases across a period from left to right.'