Which of the following elements has the greatest effective nuclear charge?

• A. Ne
• B. Mg
• C. Na
• D. Al

Answer: (B)

Verified step by step guidance

1. Understand that the effective nuclear charge (Z_eff) is the net positive charge experienced by an electron in an 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: Neon (Ne) has \(Z=10\), Sodium (Na) has \(Z=11\), Magnesium (Mg) has \(Z=12\), and Aluminum (Al) has \(Z=13\).
4. Consider the electron configuration and shielding effect for each element. Elements with more inner electrons have greater shielding, which reduces \(Z_{\text{eff}}\) experienced by the outermost electrons.
5. Analyze which element's outermost electrons experience the greatest \(Z_{\text{eff}}\) by balancing the increase in nuclear charge with the increase in shielding. This will help identify the element with the greatest effective nuclear charge.