Multiple Choice
Which statement is true about effective nuclear charge (Z_{eff})?
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10. Periodic Properties of the Elements
Periodic Trend: Effective Nuclear Charge
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Which statement is true about the effective nuclear charge (Z_ext{eff}) experienced by electrons in atoms?
A
Z_ext{eff} decreases as you move down a group in the periodic table.
B
Z_ext{eff} generally increases across a period from left to right.
C
Z_ext{eff} is unaffected by the presence of inner (core) electrons.
D
Z_ext{eff} is always equal to the atomic number (Z) for all elements.
Verified step by step guidance1
Understand that the effective nuclear charge (\(Z_{\text{eff}}\)) is the net positive charge experienced by an electron in an atom, considering both the actual nuclear charge (\(Z\)) and the shielding effect of other electrons.
Recall the formula for effective nuclear charge: \(Z_{\text{eff}} = Z - S\), where \(Z\) is the atomic number (number of protons) and \(S\) is the shielding constant representing the repulsion from other electrons, especially inner (core) electrons.
Analyze the trend across a period (left to right) in the periodic table: as \(Z\) increases by one for each successive element, the number of inner electrons (shielding) remains relatively constant, so \(Z_{\text{eff}}\) increases.
Consider the trend down a group (top to bottom): although \(Z\) increases, the number of inner electron shells also increases, which increases shielding (\(S\)), often causing \(Z_{\text{eff}}\) to increase only slightly or remain nearly constant, but not decrease significantly.
Evaluate the given statements based on these concepts: \(Z_{\text{eff}}\) is not unaffected by inner electrons (they cause shielding), and it is not always equal to \(Z\) because of shielding; the correct general trend is that \(Z_{\text{eff}}\) increases across a period from left to right.
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