## electron config. 3d and 4s

KarlaArevalo2F
Posts: 67
Joined: Tue Nov 14, 2017 3:01 am
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### electron config. 3d and 4s

Why is 3d a lower energy level than 4d after Z=20? Isn't the periodic table arranged so that energy levels increase as you go? 1s^2, 2s^2, 2p^6,3s^2,3p^6,4s^2,3d^10,4p^6....?

Megan Gianna Uy 3L
Posts: 30
Joined: Fri Sep 28, 2018 12:26 am

### Re: electron config. 3d and 4s

3d is a lower energy level because it is in the 3rd shell, whereas the 4s electrons are in the 4th shell. This means that the 4s electrons are outer electrons, further from the nucleus, and are shielded by the 3d electrons. Also, when removing an electron, the electron would be removed from the 4s orbital instead of the 3d orbital, meaning that the 4s orbital has a lower ionization energy.

Abbey Brandt 1K
Posts: 33
Joined: Fri Sep 28, 2018 12:29 am

### Re: electron config. 3d and 4s

For the 4s orbital n+ l = 4 + 0 = 4. For the 3d n+l = 3 + 2 = 5. So 4s is lower in energy so fills first.After calcium the 3d orbital falls below the 4s in terms of energy. This means the 4s electrons are lost first in chemical reactions and define the atomic radius of the atom. In summary, repulsive forces in the 3d sub shells tend to push electrons up into the larger 4s where the repulsion is less.

Josceline 3J
Posts: 33
Joined: Fri Sep 28, 2018 12:21 am

### Re: electron config. 3d and 4s

Abbey Brandt 4E wrote:For the 4s orbital n+ l = 4 + 0 = 4. For the 3d n+l = 3 + 2 = 5. So 4s is lower in energy so fills first.After calcium the 3d orbital falls below the 4s in terms of energy. This means the 4s electrons are lost first in chemical reactions and define the atomic radius of the atom. In summary, repulsive forces in the 3d sub shells tend to push electrons up into the larger 4s where the repulsion is less.

Hi, sorry I'm a bit confused. could you explain what the "n" in the n+1 stand for? from your work above it seems you substitute the energy level number in it but then instead of "+1" you added 0 and in the other a 2. Why is that?

Abbey Brandt 1K
Posts: 33
Joined: Fri Sep 28, 2018 12:29 am

### Re: electron config. 3d and 4s

Josceline 3J wrote:
Abbey Brandt 4E wrote:For the 4s orbital n+ l = 4 + 0 = 4. For the 3d n+l = 3 + 2 = 5. So 4s is lower in energy so fills first.After calcium the 3d orbital falls below the 4s in terms of energy. This means the 4s electrons are lost first in chemical reactions and define the atomic radius of the atom. In summary, repulsive forces in the 3d sub shells tend to push electrons up into the larger 4s where the repulsion is less.

Hi, sorry I'm a bit confused. could you explain what the "n" in the n+1 stand for? from your work above it seems you substitute the energy level number in it but then instead of "+1" you added 0 and in the other a 2. Why is that?

Hi Joceline!

In this context, n represents the principal quantum number and ℓ the azimuthal quantum number; the values ℓ = 0, 1, 2, 3 correspond to the s, p, d, and f labels, respectively. Does that make more sense?

Josceline 3J
Posts: 33
Joined: Fri Sep 28, 2018 12:21 am

### Re: electron config. 3d and 4s

Abbey Brandt 4E wrote:
Josceline 3J wrote:
Abbey Brandt 4E wrote:For the 4s orbital n+ l = 4 + 0 = 4. For the 3d n+l = 3 + 2 = 5. So 4s is lower in energy so fills first.After calcium the 3d orbital falls below the 4s in terms of energy. This means the 4s electrons are lost first in chemical reactions and define the atomic radius of the atom. In summary, repulsive forces in the 3d sub shells tend to push electrons up into the larger 4s where the repulsion is less.

Hi, sorry I'm a bit confused. could you explain what the "n" in the n+1 stand for? from your work above it seems you substitute the energy level number in it but then instead of "+1" you added 0 and in the other a 2. Why is that?

Hi Joceline!

In this context, n represents the principal quantum number and ℓ the azimuthal quantum number; the values ℓ = 0, 1, 2, 3 correspond to the s, p, d, and f labels, respectively. Does that make more sense?

The l is basically the different orbit levels, right?
I think I get it. Thank you so much for your help!