Why does 3d come before 4s?

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alexfwang3g
Posts: 50
Joined: Thu Jul 11, 2019 12:16 am

Why does 3d come before 4s?

Postby alexfwang3g » Wed Oct 30, 2019 11:17 pm

On the periodic table, 4s comes before 3d so shouldn't it be put before 3d in the electron config?

Sarah Zhari 1D
Posts: 87
Joined: Sat Sep 14, 2019 12:16 am

Re: Why does 3d come before 4s?

Postby Sarah Zhari 1D » Wed Oct 30, 2019 11:27 pm

When the 3d orbitals contain electrons, the 3d orbitals have a lower energy than the 4s orbitals. This is caused by electron-electron repulsions, which lower the energy.

sarahsalama2E
Posts: 148
Joined: Fri Aug 30, 2019 12:16 am

Re: Why does 3d come before 4s?

Postby sarahsalama2E » Wed Oct 30, 2019 11:31 pm

That is correct, it is also important to note that when 4s begins to fill with electrons, 4s has higher energy than 3d. So, we right 3d before 4s. Also this is for ease of removing an electron when we are forming anions.


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