Which concept explains why outer electrons experience less attraction from the nucleus than inner electrons?

• A. Ionization energy
• B. Electron affinity
• C. Nuclear charge
• D. Shielding

Answer: (D)

Shielding explains why outer electrons feel less attraction than inner ones. The nucleus pulls all electrons inward, and more protons mean a stronger pull, but the presence of inner electrons blocks part of that pull from reaching the outer electrons. This screening or shielding reduces the effective nuclear charge that outer electrons experience, so they are held less tightly in orbit. As new inner shells appear, shielding increases, lowering the net attraction on the outer electrons. Other ideas like ionization energy, electron affinity, or simply nuclear charge don’t capture this blocking effect, making shielding the correct explanation.