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Arrange these elements in order of decreasing atomic radius: Cs, Pb, Sb, Se, S.
10. Periodic Properties of the Elements
Periodic Trend: Atomic Radius
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Which atom in each group has the smallest atomic radius? Na, Si, Cl; Be, Mg, Ca?
A
Cl and Ca
B
Cl and Be
C
Si and Mg
D
Na and Be
Verified step by step guidance1
Understand that atomic radius is the distance from the nucleus of an atom to the outermost electron shell. It generally decreases across a period from left to right and increases down a group in the periodic table.
For the first group (Na, Si, Cl), identify their positions in the periodic table. Sodium (Na) is in Group 1, Silicon (Si) is in Group 14, and Chlorine (Cl) is in Group 17. All are in Period 3.
Recognize that as you move from left to right across a period, the atomic radius decreases due to the increase in nuclear charge, which pulls the electron cloud closer to the nucleus. Therefore, Cl, being furthest to the right, has the smallest atomic radius in this group.
For the second group (Be, Mg, Ca), identify their positions in the periodic table. Beryllium (Be) is in Group 2, Period 2; Magnesium (Mg) is in Group 2, Period 3; and Calcium (Ca) is in Group 2, Period 4.
Recognize that as you move down a group, the atomic radius increases due to the addition of electron shells. Therefore, Be, being at the top of the group, has the smallest atomic radius in this group.
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