All of the following are factors that affect the effective nuclear charge, Zeff, except:

• A. The principal quantum number of the valence electron
• B. The number of protons in the nucleus
• C. The number of core (inner) electrons
• D. The number of neutrons in the nucleus

Answer: (D)

Verified step by step guidance

1. Understand that the effective nuclear charge, \(Z_{eff}\), is the net positive charge experienced by an electron in a multi-electron atom. It accounts for the attraction from the nucleus and the repulsion from other electrons.
2. Recall the formula for effective nuclear charge: \(Z_{eff} = Z - S\), where \(Z\) is the atomic number (number of protons) and \(S\) is the shielding constant representing the repulsion by other electrons, especially core electrons.
3. Recognize that the number of protons (\(Z\)) directly affects \(Z_{eff}\) because more protons increase the positive charge attracting electrons.
4. Understand that the number of core (inner) electrons affects \(Z_{eff}\) because these electrons shield the valence electrons from the full nuclear charge, reducing the effective nuclear charge felt by valence electrons.
5. Note that the principal quantum number of the valence electron affects \(Z_{eff}\) indirectly because electrons in higher energy levels are farther from the nucleus and experience more shielding, but the number of neutrons does not affect \(Z_{eff}\) since neutrons are neutral particles and do not contribute to the nuclear charge.