Which of the following is an observed trend in atomic radii across the periodic table?

• A. Atomic radius decreases from left to right across a period.
• B. Atomic radius increases from top to bottom within a group.
• C. Atomic radius increases from left to right across a period.
• D. Atomic radius decreases from top to bottom within a group.

Answer: (A)

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 experienced by electrons.
3. Recognize that this increased nuclear charge pulls the electron cloud closer to the nucleus, causing the atomic radius to decrease across a period.
4. Note that down a group (top to bottom), additional electron shells are added, which increases the distance between the nucleus and the outermost electrons, leading to an increase in atomic radius.
5. Summarize the observed trends: atomic radius decreases from left to right across a period and increases from top to bottom within a group.