Key Concepts: Shielding Effect

Core Definitions

• Shielding Effect: Inner electrons block (shield) outer electrons from the full nuclear charge.
• Effective Nuclear Charge (Zeff): The net positive charge felt by valence electrons after shielding: Zeff = Z − S.
• More Shielding: As you go DOWN a group, more inner electron shells increase shielding, so outer electrons are held less tightly.
• Across a Period: Shielding stays roughly the same, but nuclear charge increases, so Zeff increases.
• Effect on Atomic Radius: Greater shielding → larger atomic radius (electrons are farther from nucleus).
• Effect on Ionization Energy: Greater shielding → lower ionization energy (easier to remove outer electrons).