Which of the following elements will have the greatest effective nuclear charge?

• A. Si
• B. Al
• C. Na
• D. Mg

Answer: (A)

Verified step by step guidance

1. Understand that effective nuclear charge (Z_eff) is the net positive charge experienced by an electron in a multi-electron atom. It accounts for the actual nuclear charge (number of protons) minus the shielding effect caused by other electrons.
2. 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 electron repulsion.
3. Compare the atomic numbers of the given elements: Na (11), Mg (12), Al (13), and Si (14). Since all are in the same period, the shielding effect is relatively similar because electrons are added to the same principal energy level.
4. Since shielding is similar across these elements, the effective nuclear charge increases with increasing atomic number. Therefore, the element with the highest atomic number will have the greatest \(Z_{\text{eff}}\).
5. Conclude that silicon (Si), having the highest atomic number among the options, experiences the greatest effective nuclear charge.