Shielding (Screening) Effect is the reduction in nuclear attraction on valence electrons due to the presence of inner shell electrons.

• The effectiveness of shielding depends on the shape of the orbital. Orbitals closer to the nucleus screen more effectively.
• Order of Shielding: $s>p>d>f$.
• $s$-electrons have the highest penetration power and spherical symmetry, providing the most 'shadow' or protection from the nuclear charge for electrons in outer shells.