Why does chlorine's noble gas configuration use Ne instead of Ar?

[tica86]

Can someone PLEASE explain the electron configuration for Chlorine.
I know it is
1s^2, 2s^2, 2p^6, 3s^2, 3p^5

and that the noble gas configuration is
[Ne]-3s2-3p5

but what I don't understand is why is it Ne and not Ar since Cl gains one electron 3p^6, that is Ar not Ne, Ne is 1s^2, 2s^2, 2p^6 :/ I'm very confused!
Can someone please explain, thanks!

 

[Coto]

I think you're confusing a couple of things here.

The "noble gas configuration" that you listed is a short-hand notation for $1s^2 2s^2 2p^6 3s^2 3p^5$, it is **not** the configuration for the chlorine ion. Notice that the [Ne] electron configuration is $1s^2 2s^2 2p^6$ so instead of writing that entire long expression for chlorine, we can write it as [Ne] $3s^2 3p^5$.

If you wanted to write the electron configuration for the chlorine *ion* (Cl$^-$), then you could simply write [Ar], since the electron configuration is the same as the Argon atom.

 

[tica86]

I think you're confusing a couple of things here.

The "noble gas configuration" that you listed is a short-hand notation for $1s^2 2s^2 2p^6 3s^2 3p^5$, it is **not** the configuration for the chlorine ion. Notice that the [Ne] electron configuration is $1s^2 2s^2 2p^6$ so instead of writing that entire long expression for chlorine, we can write it as [Ne] $3s^2 3p^5$.

If you wanted to write the electron configuration for the chlorine *ion* (Cl$^-$), then you could simply write [Ar], since the electron configuration is the same as the Argon atom.

Ok, thanks!

I have another question for the Pb configuration, if you could answer it.

I know it's
1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^2, 3d^10, 4p^6, 5s^2, 4d^10, 5p^6, 6s^2, 4f^14, 5d^10, 6p^2


My question is why after 6s^2 does it go directly to 4f^14 why is it not 6s^2, 5d^10, 6p^2 and NO 4f^14?? If by 6p^2 you reach Pb...


****Also for Uranium it's
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f14 5d10 6s2 6p6 5f3 6d1 7s2

Again I don't understand the "jump" from 5p6 to 4f14 5d10 6s2 6p6 5f3 6d1 7s2?

 

[Coto]

The jump is simply due to the fact that the 4f level is at a lower energy than the 5d level, just as the 5d level is lower than the 6s level, etc.

The reason is due to the idea of electron shielding, and electron penetration .. google these concepts if you want to know more.

 

[Borek]

Also google Aufbau principle.