Which atom has the smallest atomic radius?

• A. Na
• B. F
• C. Cl
• D. Li

Answer: (B)

Verified step by step guidance

1. Understand that atomic radius generally decreases across a period (left to right) on the periodic table because the number of protons increases, pulling electrons closer to the nucleus.
2. Identify the positions of the given atoms (Na, F, Cl, Li) on the periodic table: Na and Li are in Group 1, while F and Cl are in Group 17; Na and Cl are in Period 3, Li and F are in Period 2.
3. Compare atoms in the same period first: between Li and F (both in Period 2), F has more protons, so it has a smaller atomic radius than Li.
4. Compare atoms in different periods: atoms in Period 2 generally have smaller radii than those in Period 3 because electrons are closer to the nucleus with fewer energy levels.
5. Conclude that among Na, F, Cl, and Li, fluorine (F) has the smallest atomic radius due to its position in Period 2 and Group 17, meaning it has a high effective nuclear charge pulling electrons closer.