What is the effective nuclear charge (Z_eff) experienced by a 3s electron in a sodium atom (Na)?

• A. Approximately 11
• B. Approximately 10
• C. Approximately 0.9
• D. Approximately 2.2

Answer: (D)

Verified step by step guidance

1. Identify the atomic number (Z) of sodium (Na), which is 11. This represents the total number of protons in the nucleus and the total positive charge attracting the electrons.
2. Determine the electron configuration of sodium: 1s² 2s² 2p⁶ 3s¹. The electron of interest is the 3s electron, the outermost electron.
3. Calculate the shielding constant (S) by considering the electrons that are closer to the nucleus than the 3s electron. These include the 1s², 2s², and 2p⁶ electrons, totaling 10 electrons that shield the 3s electron from the full nuclear charge.
4. Use Slater's rules or a simplified approach to estimate the shielding effect. For the 3s electron, the inner 10 electrons effectively shield most of the nuclear charge, so S ≈ 8 to 10 depending on the method, but here we consider all 10 inner electrons as shielding.
5. Calculate the effective nuclear charge using the formula: \(Z_{\text{eff}} = Z - S\). Substitute the values to find \(Z_{\text{eff}}\) experienced by the 3s electron in sodium.