Why does the 4s orbital come before the 3d?

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Mario Reyes 1C
Posts: 45
Joined: Fri Apr 06, 2018 11:04 am

Why does the 4s orbital come before the 3d?

Postby Mario Reyes 1C » Fri Apr 27, 2018 3:33 pm

If I heard correctly in class, the 4s orbital comes before 3d only for elements with 20 electrons or less. Can somebody explain why?

Joanna Pham - 2D
Posts: 113
Joined: Fri Apr 06, 2018 11:04 am

Re: Why does the 4s orbital come before the 3d?

Postby Joanna Pham - 2D » Fri Apr 27, 2018 3:44 pm

I was confused about this too. I don't understand the exact reason why 3d comes before 4s when writing the electron configuration.

Jennifer Tuell 1B
Posts: 34
Joined: Fri Apr 06, 2018 11:05 am

Re: Why does the 4s orbital come before the 3d?

Postby Jennifer Tuell 1B » Fri Apr 27, 2018 5:10 pm

3d is at a lower energy level than 4s therefore it comes before it in the electron configuration because it going from lowest to highest energy level.

Nandhini_2K
Posts: 60
Joined: Fri Apr 06, 2018 11:03 am

Re: Why does the 4s orbital come before the 3d?

Postby Nandhini_2K » Fri Apr 27, 2018 7:31 pm

The 4s orbitals are lower than 3d.
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Joanna Pham - 2D
Posts: 113
Joined: Fri Apr 06, 2018 11:04 am

Re: Why does the 4s orbital come before the 3d?

Postby Joanna Pham - 2D » Fri Apr 27, 2018 9:46 pm

I am curious,why exactly does 3d have a lower energy level than 4s?

tmehrazar
Posts: 39
Joined: Fri Apr 06, 2018 11:04 am

Re: Why does the 4s orbital come before the 3d?

Postby tmehrazar » Sat Apr 28, 2018 11:23 am

the 4s orbitals have lower energy than the 3d orbitals not the other way around, some things online say that s-orbitals are more penetrating than d-orbitals so i think that may be why

MadelynNguyen1F
Posts: 59
Joined: Fri Apr 06, 2018 11:04 am

Re: Why does the 4s orbital come before the 3d?

Postby MadelynNguyen1F » Sat Apr 28, 2018 1:51 pm

I think 4s might fill up first because of electron repulsion. I was looking online and it said that was related to the fact that 4s fills up before 3d.

Alejandro Salazar 1D
Posts: 31
Joined: Fri Sep 29, 2017 7:05 am

Re: Why does the 4s orbital come before the 3d?

Postby Alejandro Salazar 1D » Sat Apr 28, 2018 8:50 pm

The electron configuration for Cr is different, by having the 3d come first before the 4s because having two electrons in the 4s makes the orbital more unstable because of electron repulsion


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