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Multiple Choice
Which of the following elements has atoms that most likely experience the greatest shielding effect?
A
Cs
B
Rb
C
K
D
Na
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1
Understand the concept of shielding effect: Shielding occurs when inner electrons reduce the effective nuclear charge felt by the outer (valence) electrons. The more inner electron shells an atom has, the greater the shielding effect experienced by its outer electrons.
Identify the elements given: Cs (Cesium), Rb (Rubidium), K (Potassium), and Na (Sodium) are all alkali metals in Group 1 of the periodic table, but they differ in their principal energy levels (electron shells).
Determine the period (row) of each element: Na is in period 3, K is in period 4, Rb is in period 5, and Cs is in period 6. As you move down the group, the number of electron shells increases.
Relate the number of electron shells to shielding: More electron shells mean more inner electrons, which increases the shielding effect on the valence electrons.
Conclude that Cs, being the element with the highest principal energy level (period 6), has the greatest number of inner electron shells and therefore its valence electrons experience the greatest shielding effect.