3d And 4s Orbital Energy Levels  [ENDORSED]

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Nisarg Shah 1C
Posts: 54
Joined: Sat Jul 22, 2017 3:00 am

3d And 4s Orbital Energy Levels

Postby Nisarg Shah 1C » Fri Oct 20, 2017 5:44 pm

How can 4s orbitals be lower than 3d orbitals in some cases, while in other cases they are not? For example, the electron configuration for Ca is [Ar]4s2, but for Sc, it is [Ar]3d1,4s2. Why is it not [Ar]4s2,3d1? I'm confused as to how 4s can have lower energy for some atoms, and higher energy for others.

Tatiana R Dis 3E
Posts: 20
Joined: Fri Sep 29, 2017 7:07 am

Re: 3d And 4s Orbital Energy Levels

Postby Tatiana R Dis 3E » Fri Oct 20, 2017 5:47 pm

I'm confused about this as well. Would the configuration for Ti (Titanium) be Ti: [Ar] 3d2 4s2?

Christine Wastila 1H
Posts: 61
Joined: Fri Sep 29, 2017 7:04 am

Re: 3d And 4s Orbital Energy Levels  [ENDORSED]

Postby Christine Wastila 1H » Fri Oct 20, 2017 6:15 pm

4s is lower energy than 3d for Ca and K because they do not have any electrons in the d block. After the 4s orbital is occupied and electrons enter the 3d state, 3d is then lower energy than 4s. That is why electrons in the 3d block are listed before those in 4s when writing the electron configuration for elements with electrons in the 3d state. For example- Scandium: [Ar] 3d1 4s2. And yes, Titanium would be Ti: [Ar]: 3d2 4s2.

Timothy Kim 1B
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

Re: 3d And 4s Orbital Energy Levels

Postby Timothy Kim 1B » Sat Oct 21, 2017 5:27 pm

Under certain circumstances is the 3d state lower in energy.
Once the 4s state is occupied and the electron enters the 3d state, then the 3d state is lower in energy than 4s. If the electron hasn't reached 3d yet, then 4s is written first.


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