If the atomic radius of aluminum is 0.143 nm, which element is expected to have a smaller atomic radius than aluminum?

• A. Magnesium (Mg)
• B. Sodium (Na)
• C. Potassium (K)
• D. Silicon (Si)

Answer: (D)

Verified step by step guidance

1. Understand that atomic radius generally decreases across a period (left to right) in the periodic table due to increasing nuclear charge pulling electrons closer to the nucleus.
2. Identify the position of aluminum (Al) in the periodic table: it is in period 3, group 13.
3. Compare the elements given: Magnesium (Mg), Sodium (Na), and Potassium (K) are all to the left of aluminum in the periodic table, meaning they have larger atomic radii.
4. Recognize that Silicon (Si) is to the right of aluminum in the same period, so it experiences a greater effective nuclear charge, resulting in a smaller atomic radius than aluminum.
5. Conclude that among the options, Silicon (Si) is expected to have a smaller atomic radius than aluminum due to its position in the periodic table.