Multiple Choice
Which factor is primarily responsible for the decrease in atomic radius as you move from left to right across a period in the periodic table?
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10. Periodic Properties of the Elements
Periodic Trend: Atomic Radius
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Which neutral atom below has the largest atomic radius?
A
Mg
B
Na
C
K
D
Al
Verified step by step guidance1
Recall that atomic radius generally increases as you move down a group (column) in the periodic table because additional electron shells are added, increasing the size of the electron cloud.
Recall that atomic radius generally decreases as you move from left to right across a period (row) in the periodic table because the effective nuclear charge increases, pulling electrons closer to the nucleus.
Identify the positions of the given elements (Mg, Na, K, Al) on the periodic table: Na and Mg are in period 3, Al is also in period 3, and K is in period 4, which is one row below the others.
Since K is in the period below Na, Mg, and Al, it has an additional electron shell, which increases its atomic radius compared to the others.
Therefore, based on periodic trends, the neutral atom with the largest atomic radius among the given options is K.
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