Which statement is true about electron shielding of nuclear charge?

• A. Inner electrons shield outer electrons from the full positive charge of the nucleus.
• B. Electron shielding causes the effective nuclear charge to increase for outer electrons.
• C. Valence electrons are more effective at shielding than core electrons.
• D. Electron shielding increases as you move across a period from left to right.

Answer: (A)

Verified step by step guidance

1. Understand the concept of electron shielding: Electron shielding occurs when inner (core) electrons repel outer (valence) electrons, reducing the full positive charge from the nucleus felt by the outer electrons.
2. Recognize that inner electrons are located closer to the nucleus and thus block or 'shield' the outer electrons from the full nuclear charge, effectively lowering the attraction between the nucleus and the valence electrons.
3. Recall that effective nuclear charge (\(Z_{eff}\)) is the net positive charge experienced by an electron and is calculated as \(Z_{eff} = Z - S\), where \(Z\) is the atomic number and \(S\) is the shielding constant representing the number of electrons between the nucleus and the electron in question.
4. Note that valence electrons are less effective at shielding because they are farther from the nucleus and do not block the nuclear charge as effectively as core electrons do.
5. Understand that as you move across a period from left to right, the number of protons increases, but shielding does not increase significantly because electrons are added to the same energy level, so effective nuclear charge increases rather than shielding.