r2R2 Shielding 1s 4f 4d494s Penetration: 4s>4p>4d>4f r A 4s electron penetrates the 1s orbital better than a 4p electron IV-11Shielding A 4s electron penetrates the 1s orbital better than a 4p electron r2R2 r Penetration: 4s > 4p > 4d > 4f 1s 4f 4d 4s 4p IV-11