How does shielding affect electrons in the same energy level?
Jenkin says Shielding is not a particularly easy concept to understand, but this may help. Each electron is repelled by the other electrons in the atom and so is less tightly bound to the nucleus than it would be if the other electrons were not there. We can say that each electron is shielded from the full attraction of the nucleus by the other electrons. Within a shell, an s electron penetrates closer to the nucleus than a p (or d) electron of the same shell. So an s electron is less shielded from the nucleus by the atoms other electrons, meaning that an s electron has a slightly lower energy than a p electron of the same shell. Similarly, p electrons approach the nucleus more closely than d electrons so the shielding effect is less for p than for d electrons. This has important consequences for the sequence in which orbitals are filled. For example, the effect of shielding means that a 4s orbital may have a lower energy than a 3d, so the electron configuration of a potassium atom (in
