Shielding r2R2 1s 3d 3P39 Penetration: 3s>3p>3d r A 3s electron penetrates the 1s orbital better than a 3p electron IV-10Shielding A 3s electron penetrates the 1s orbital better than a 3p electron r2R2 r 1s 3d 3p 3s Penetration: 3s > 3p > 3d IV-10