[kauzs-17]

I'm studying for the ACS standardized test.
In lecture, we learned that the electron configuration goes like this: 1s2 2s2 2p6 3s2 3p6 4s2 3d10, and so on. However, according to the ACS study guide, it's 1s2 2s2 2p6 3s2 3p6 3d10 4s2. Why this difference?

[Hunter2]

They don't take care of the energy levels. The first one is correct.

[kauzs-17]

According to the guide, the second is correct. Should I just use their method for this test then disregard it?

[Hunter2]

I dont know what your teacher expect. Both can be used. The first one is more accurate.

[Borek]

If I tell you I have $3 in my left pocket, and $5 in my right pocket, then someone else says they have have $5 in the right pocket, and $3 in their left pocket, is the $$ configuration in our pockets identical, or different?

Order in which they are listed doesn't matter, what matters is how the orbitals are filled. 4s² 3d¹⁰ suggests 4s was filled first, then 3d - but regardless of which was filled first, the final configurations are identical. It is just a matter of convention how they are listed, and there is no convention that everyone agrees on.

[kauzs-17]

If I tell you I have $3 in my left pocket, and $5 in my right pocket, then someone else says they have have $5 in the right pocket, and $3 in their left pocket, is the $$ configuration in our pockets identical, or different?

Order in which they are listed doesn't matter, what matters is how the orbitals are filled. 4s² 3d¹⁰ suggests 4s was filled first, then 3d - but regardless of which was filled first, the final configurations are identical. It is just a matter of convention how they are listed, and there is no convention that everyone agrees on.

Fair enough. However, let's say instead of having 30 electrons we had 28, which would be the difference between 4s² 3d⁸ or 3d¹⁰ and no 4s. Would it still be the same?

Thanks for your answer.

[Borek]

Fair enough. However, let's say instead of having 30 electrons we had 28, which would be the difference between 4s² 3d⁸ or 3d¹⁰ and no 4s. Would it still be the same?

No. 3d¹⁰ 4s⁰ and 3d⁸ 4s² are different - same number of electrons, but different configuration.

[Hunter2]

If I tell you I have $3 in my left pocket, and $5 in my right pocket, then someone else says they have have $5 in the right pocket, and $3 in their left pocket, is the $$ configuration in our pockets identical, or different?

Order in which they are listed doesn't matter, what matters is how the orbitals are filled. 4s² 3d¹⁰ suggests 4s was filled first, then 3d - but regardless of which was filled first, the final configurations are identical. It is just a matter of convention how they are listed, and there is no convention that everyone agrees on.

Fair enough. However, let's say instead of having 30 electrons we had 28, which would be the difference between 4s² 3d⁸ or 3d¹⁰ and no 4s. Would it still be the same?

Thanks for your answer.

You can only write 4s² 3 d⁸ or 3d⁸ 4s² but don't move electrons in other Orbitales.

[kauzs-17]

Fair enough. However, let's say instead of having 30 electrons we had 28, which would be the difference between 4s² 3d⁸ or 3d¹⁰ and no 4s. Would it still be the same?

No. 3d¹⁰ 4s⁰ and 3d⁸ 4s² are different - same number of electrons, but different configuration.

That's where I'm confused. I don't want to miss a question because I did 3d before I did 4s as opposed to 4s before 3d.

[Hunter2]

Borek explained it with the $ in the pocket.
if 2 $ in the right pocket and 3 $ in the left pocket or vise versa is the same its together 5 $.

So if you write d⁸ s² or s⁴ d⁸ is also more or less the same. The electrons are in the right orbitals, but if you write d⁹ 4s then its different. In this case the differrent would be also 4 s and d⁹.

[kauzs-17]

I've always been taught you have to fill one before moving on. d orbitals require 10 electrons, so how could I only put 8 before moving on to 4s?

[kauzs-17]

Or are you actually filling 4s before 3d but writing it as 3d8 4s2?

[Hunter2]

Nature is different.  Look in the periodic system  of elements. until element Argon everything is fine. Argon has shell 3 what can take 18 electrons maximum. But there is a rule that not more as 8 electrons on the outer shell. So for potassium and calcium shell 4 will be started with 4 s and 4 s². With Scandium the d-Orbitals of shell 3 will be started and filled until zinc. d¹ to d¹⁰ after that shell 4 will be continued with th p-Orbitals.

[Corribus]

kauzs-17:

Filling order is complicated. Maybe this will help you understand: http://www.chemguide.co.uk/atoms/properties/3d4sproblem.html