Multiple Choice
Which of the following best describes how atomic radius changes as you move down a group in the periodic table?
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10. Periodic Properties of the Elements
Periodic Trend: Atomic Radius
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Which of the following elements has the smallest atomic radius?
A
Cl
B
Na
C
Al
D
Mg
Verified step by step guidance1
Recall that atomic radius generally decreases across a period (left to right) in the periodic table due to increasing effective nuclear charge, which pulls electrons closer to the nucleus.
Identify the period and group of each element: Na (Sodium) is in period 3, group 1; Mg (Magnesium) is in period 3, group 2; Al (Aluminum) is in period 3, group 13; Cl (Chlorine) is in period 3, group 17.
Since all elements are in the same period (period 3), compare their positions from left to right: Na < Mg < Al < Cl in terms of increasing atomic number and effective nuclear charge.
Understand that as you move from left to right across a period, the atomic radius decreases because the number of protons increases, pulling the electron cloud closer without significant increase in electron shielding.
Conclude that Cl, being the farthest to the right in period 3 among the given elements, has the smallest atomic radius.
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