Thread: Electron shell

When they say "filled electron shell" do they mean subshell instead? I mean, look at Argon. Its third shell isn't even full and yet it's a noble gas.

do they mean subshell instead?

Depends on the context, in this case yes.

Ah, okay thanks and sorry for the poor grammar. I'm currently in a rush. I edited them btw.

Originally Posted by molecool

When they say "fill up an electron shell" do they mean subshell instead? I mean, look at argon. Its third shell isn't even full.

They mean fill it up from the lowest energy level first, until you have enough electrons for electrical neutrality.

The tricky bit is that, as the nuclear charge goes up and you fill the lower orbitals, the relative energies of the higher levels start to change. This is due to something called "penetration" and "shielding". Specifically, because electrons in an s orbital can go right up to the nucleus, whereas those in p,d or f orbitals cannot, electrons in an outer s orbital are still somewhat exposed to the effect of the full nuclear charge, whereas those in p, d and f orbitals are more completely "shielded" by the inner completed shells of electrons. The s orbitals are said to "penetrate" this shield.

So, as you go up in nuclear charge (to higher atomic numbers), the 4s (for example) gets pulled down in energy to a level lower than the 3d. This is why the 1st row of transition elements starts where its does. Only once 4s is full does 3d start to be filled.

As exchemist says, it is down to penetration and shielding, I gave an explanation and a link desribing this concepts here: orbital energy level of he+

Originally Posted by exchemist

Originally Posted by molecool

When they say "fill up an electron shell" do they mean subshell instead? I mean, look at argon. Its third shell isn't even full.

They mean fill it up from the lowest energy level first, until you have enough electrons for electrical neutrality.

The tricky bit is that, as the nuclear charge goes up and you fill the lower orbitals, the relative energies of the higher levels start to change. This is due to something called "penetration" and "shielding". Specifically, because electrons in an s orbital can go right up to the nucleus, whereas those in p,d or f orbitals cannot, electrons in an outer s orbital are still somewhat exposed to the effect of the full nuclear charge, whereas those in p, d and f orbitals are more completely "shielded" by the inner completed shells of electrons. The s orbitals are said to "penetrate" this shield.

So, as you go up in nuclear charge (to higher atomic numbers), the 4s (for example) gets pulled down in energy to a level lower than the 3d. This is why the 1st row of transition elements starts where its does. Only once 4s is full does 3d start to be filled.

Actually what I meant was for example, sodium has a high tendency to lose an electron in order to obtain a "filled electron shell", and do they mean subshell instead, because Argon's third shell isn't even full and yet it's a noble gas because of its filled subshells. Though this is already answered by PhDemon previously. Anyway, still, thanks for the answer. At least it's what I'm looking for too.

I may have answered your question but exchemist has introduced why this is the case. The "penetration and shielding" effects he mentioned are why the 3d orbitals are much higher in energy than the 3p in Argon and in turn this is why the 3p⁶ configuration is particularly stable.

I think that in addition to "penetration and shielding", one should also consider the change in energy with respect to the change in electron configuration to see why it is specifically the filling of the p orbitals that leads to the noble gas configuration rather than the filling of some other orbitals. The filling of a set of orbitals does lead to a relatively stable configuration in general, but it is the energy gap between the filling of p and the following s that makes the filling of p especially stable.

True, that is an effect that is certainly important but I didn't think the level of the question warranted going into it.