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[Faisal Alshamaa - 1L]

Which of the following statements are true for many- electron atoms? If false, explain why. (a) The effective nuclear charge Z-eff is independent of the number of electrons present in an atom. (b) Electrons in an s-orbital are more effective than those in other orbitals at shielding other electrons from the nuclear charge because an electron in an s-orbital can penetrate to the nucleus of the atom. (c) Electrons having l = 2 are better at shielding than electrons having l = 1. (d) Z-eff for an electron in a p-orbital is lower than for an electron in an s-orbital in the same shell.

Hello,
So I do remember learning about this in lecture and how lower orbitals shield the outside orbitals and electrons from experiencing that pull by the nucleus. Is this what is referred to by the effective nuclear charge? The pull of the nucleus on the electrons?
Also I am a bit confused on what it means when it says that electrons penetrate the nucleus? is this meant literally because I thought that electrons simply exist around the nucleus and never actually touch it?

Any help would be appreciated :) thank you!

[Jaquelinne Rodriguez-Lopez 1L]

I don't recall professor Lavelle speaking about Zeff in class. However, he did speak about electrostatic attraction, where the electrons closer to the nucleus shield the nucleus' charge from outer electrons.

[Mohamad 1J]

So Zeff can be measured by
Zeff = Z - S
with Z being the atomic # and S being the number of inner shell electrons. That is why a) is false because the number of electrons will determine the Zeff.

As for electron penetration, that is just saying how close an electron can get to the nucleus. Although s orbitals do have the uniqueness of having a nonzero chance of being found in the nucleus itself.