Which of the following best describes the general trend for atomic radius across a period and down a group in the periodic table?

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

Answer: (D)

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. Recall that across a period (left to right) in the periodic table, the number of protons in the nucleus increases, which increases the effective nuclear charge pulling electrons closer, thus decreasing atomic radius.
3. Recognize that down a group (top to bottom), new electron shells are added, increasing the distance between the nucleus and the outermost electrons, which increases atomic radius despite the increase in nuclear charge.
4. Combine these concepts to conclude that atomic radius generally decreases across a period due to increasing nuclear charge and increases down a group due to the addition of electron shells.
5. Therefore, the general trend is: atomic radius decreases across a period and increases down a group.