# Question #44238

Aug 17, 2014

It took a bit of reading, but I think I see the source of our misunderstandings.

The article says, "Electrons in an $s$ orbital have a greater shielding power than electrons in a $p$ or $d$ orbital of that same shell … For example, consider an atom of carbon whose electron configuration is $1 {s}^{2} 2 {s}^{2} 2 {p}^{2}$. The two electrons in the $1 s$ orbital of C will do a better job of shielding the two electrons in the $2 p$orbitals than they will of shielding the two electrons in the $2 s$ orbital."

The article is really saying, "Electrons in an $s$ orbital have a greater shielding power than electrons in a $p$ or $d$ orbital of that same shell for electrons in the next higher shell".

It isn't saying that a $2 s$ electron is more effective at shielding another $2 p$ electron than a $2 s$ electron.

It is saying that a $1 s$ electron is more effective at shielding a $2 p$ than a $2 s$ electron.

This explains the dip in ionization energy on going from Be to B. When you go from a $2 s$ orbital in Be to a $2 p$ orbital in B, the $1 s$ electrons are more effective at shielding the $2 p$ electron of B.