Which of the following correctly ranks the atoms Li, Al, Be, Ba, and O in order of increasing atomic radius (smallest to largest)?

• A. Li, Be, O, Al, Ba
• B. O, Li, Be, Al, Ba
• C. Be, O, Li, Al, Ba
• D. O, Be, Li, Al, Ba

Answer: (D)

Verified step by step guidance

1. Recall that atomic radius generally decreases across a period (left to right) on the periodic table due to increasing nuclear charge pulling electrons closer, and increases down a group (top to bottom) because additional electron shells are added.
2. Identify the positions of the given elements on the periodic table: O (oxygen) is in period 2, group 16; Be (beryllium) is in period 2, group 2; Li (lithium) is in period 2, group 1; Al (aluminum) is in period 3, group 13; Ba (barium) is in period 6, group 2.
3. Compare elements in the same period first: between O, Be, and Li (all in period 2), atomic radius increases from right to left, so O < Be < Li.
4. Next, compare elements in different periods: Al is in period 3, so it has a larger radius than period 2 elements due to an additional electron shell, and Ba is in period 6, so it has the largest radius among all due to even more electron shells.
5. Combine these observations to rank the atoms in order of increasing atomic radius: O (smallest), then Be, then Li, followed by Al, and finally Ba (largest).