Fe2+ Electron config paradox

[banner18]

someone want to explain why Fe2+ has a electron config of [Ar]3d6???

according to kaplan: the greater nuclear charge offsets the destabilizing effects that would force it to fill 4s2 before the 3d orbital. I dont get this at all because Cr has a config of [Ar]3s1 4d5....

the only reasonable explanation i can think of is that since Fe2+ has more protons than Cr it will pull the 3d orbital in and shield the 4s better, allowing the 4s2 to leave. there is no way i could anticipate or think about such issues on test day.. fml

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[Dimkin]

someone want to explain why Fe2+ has a electron config of [Ar]3d6???

according to kaplan: the greater nuclear charge offsets the destabilizing effects that would force it to fill 4s2 before the 3d orbital. I dont get this at all because Cr has a config of [Ar]3s1 4d5....

the only reasonable explanation i can think of is that since Fe2+ has more protons than Cr it will pull the 3d orbital in and shield the 4s better, allowing the 4s2 to leave. there is no way i could anticipate or think about such issues on test day.. fml

It is better to take off the two electrons from the 4s orbital rather than from the 3d orbital. This is because if you take off the electrons from the 3d orbital you will have only have 3 electrons in 3d. Remember from chemistry those boxes. S orbital has 1 box [ ]. P orbital has 3 boxes [ ] [ ] [ ]. And the d orbital has 5 boxes [ ] [ ] [ ] [ ] [ ].

So how does the 3d orbital look like for Fe?

[l ] [l ] [l ] [l ] [l ]<----- like this.
There is an electron in every single box. To have a stable configuration we want them to be all filled, or not filled at all or the third best thing is to have it half full. If we take off two electrons from the 3d it will be far more unstable cause it will only have 3 electrons in the 3d orbital which is neither of the three favorable options. We take off from the 4s orbital because it will become empty and the 3d orbital will be half full.

This is the basic concept. The most important thing to remember is the stability. Zn 2+ is very similar....the electrons that we take of are from the s orbital not from the d.

If you want me to clarify it more. I would be glad to use some more technical terms.

 

[MedChallenge]

It is better to take off the two electrons from the 4s orbital rather than from the 3d orbital. This is because if you take off the electrons from the 3d orbital you will have only have 3 electrons in 3d. Remember from chemistry those boxes. S orbital has 1 box [ ]. P orbital has 3 boxes [ ] [ ] [ ]. And the d orbital has 5 boxes [ ] [ ] [ ] [ ] [ ].

So how does the 3d orbital look like for Fe?

[l ] [l ] [l ] [l ] [l ]<----- like this.
There is an electron in every single box. To have a stable configuration we want them to be all filled, or not filled at all or the third best thing is to have it half full. If we take off two electrons from the 3d it will be far more unstable cause it will only have 3 electrons in the 3d orbital which is neither of the three favorable options. We take off from the 4s orbital because it will become empty and the 3d orbital will be half full.

This is the basic concept. The most important thing to remember is the stability. Zn 2+ is very similar....the electrons that we take of are from the s orbital not from the d.

If you want me to clarify it more. I would be glad to use some more technical terms.

Isn't this explanation for Mn2+ and not Fe2+?

 

[DrJMR]

So anytime you ionize something, you ALWAYS remove from the highest E orbital, correct?

But when you're looking for an element in it's natural configuration (ie. Cu, Cr, Mo), Aufbau's principle can be violated?

 

[banner18]

Yup that makes perfect sense for Mn2+.

the question here for Fe2+, is it better to have 2 half-filled orbitals or 1 uneven d orbital? It seems intuitive to have 2 half-filled orbitals...

If you look at cobalt (Co3+) you run into the same issue.. Would it be [Ar] 3d6 or would it be [Ar] 4s1 3d5? ARRRRRGHHHH guess what its [Ar]4s1 3d5.... I DONT UNDERSTANDD..

 

[banner18]

If you look at cobalt (Co3+) you run into the same issue.. Would it be [Ar] 3d6 or would it be [Ar] 4s1 3d5? ARRRRRGHHHH guess what its [Ar]4s1 3d5.... I DONT UNDERSTANDD..

ooh did some digging.. i guess it is [Ar]3d6, so i think my explanation of the "more positive" nuclear charge and shielding does work. thanks for helping me think it through!

 

[GreenRabbit]

I'd rest easy knowing that the MCAT will explain all of this to you in a passage if it asks for this level of detail.

 

[Dimkin]

Isn't this explanation for Mn2+ and not Fe2+?

I just realized it. Yes, you are right. Sorry, I hope I didn't confuse anybody.
My apologize

 

[MedChallenge]

I just realized it. Yes, you are right. Sorry, I hope I didn't confuse anybody.
My apologize

Not a problem..just making sure I wasn't completely lost!