1. Electron Configurations

2. Shielding and Penetration
Orbitals with radial probability closer to the nucleus are more penetrating.
The closer, more penetrating orbitals, are shielding the further orbitals from the nucleus.
Energy levels and orbitals are different distances from the nuclei. Those lowest energy and clo
Here I have the radial probability graphs of the first three s orbitals shown. This shows the distance from the nuclei that the electrons in the orbital are located. You can see the higher in energy, the further away most of the electron density is. This shows us that lower energy levels are what we call more penetrating, or further from the nucleus. We can also here that in between the 2s orbital and the nuclei are located the majority of the 1S electrons. These electrons will block the 2s electrons from feeling as much of the nuclear charge, this concept is called shielding.
We’ll extend this out to p and d orbitals in later videos as well.

3. Energies of Orbitals E Questions:
Hydrogenei
Everything other than Hydrogen
Now lets draw out more of the orbitals in the correct order of energy. I have drawn out two diagrams, one for hydrogen and hydrogen like ions and one for everything else. I’ll talk about an easier way to remember this order in a moment.
First what is the main difference between the two? In the one electron systems all of the subshells in an energy level are “degenerate” or of the same energy level. In the multi electron system the subshells are different in energy. Lets think about why this would be different? In multi electron systems there are electrons in the lower energy levels and those shield the higher energy levels. In one electron systems there aren’t electrons in the lower shells so there is no shielding.
Now lets think about hydrogen and other one electron systems. I drew out energy levels for higher than the 1s orbital, is this possible even though there is only one electron? *pause*** Sure its possible, even though only the 1s is occupied in the ground state, as we saw in earlier videos we can promote the electron to a higher energy level. Therefore the other orbitals certainly still exist, they just aren’t filled.
Questions:
What is the difference between the two?
Why do you think hydrogen is different?

4. Energies of Orbitals E
Hydrogenei
Everything other than Hydrogen
Now lets draw out more of the orbitals in the correct order of energy. I have drawn out two diagrams, one for hydrogen and hydrogen like ions and one for everything else. I’ll talk about an easier way to remember this order in a moment.
First what is the main difference between the two? In the one electron systems all of the subshells in an energy level are “degenerate” or of the same energy level. In the multi electron system the subshells are different in energy. Lets think about why this would be different? In multi electron systems there are electrons in the lower energy levels and those shield the higher energy levels. In one electron systems there aren’t electrons in the lower shells so there is no shielding.
Now lets think about hydrogen and other one electron systems. I drew out energy levels for higher than the 1s orbital, is this possible even though there is only one electron? *pause*** Sure its possible, even though only the 1s is occupied in the ground state, as we saw in earlier videos we can promote the electron to a higher energy level. Therefore the other orbitals certainly still exist, they just aren’t filled.
Question: Here I have draw hydrogen with atomic orbitals higher than 1. Is this correct? Why or why not?

5. Energies in Relation to Periodic Table4f
Here is an expanded version of the periodic table. This version doesn’t fit well into book covers and isn’t a favorite amongst publishers because of that, however it’s the most useful for the filling in of energy levels and making electron configurations. So think of this whenever you look at your periodic table in the book. This way we can make electron configurations without having to memorize the order. Lets first do a few examples filling into the chart on the previous page. Once you have some examples we’ll come back to the periodic table and walk through a few more quickly.

6. 1s 2p 3d 4f Find the electron configuration of: Oxygen
What ion do you think oxygen likes to be?
Why? Give the electron configuration of the ion in your explanation.
1s22s22p4 OR [He] 2s22p4
-2 ion
1s22s22p6 OR [He] 2s22p6 OR [Ne] 3d 4f 1s 2p

7. What is the electron Configuration for selenium
More than one answer may be possible
A) [Ar]4s23d104p4
B) [Ar]4s24p4
C) [Ar]4s24d104p4
D) [Ar]4s23d103p4
E) None of the above

8. What is the electron Configuration for the fluorine ion?
More than one answer may be possible
A) [He]2s22p5
B) [He]2s22p6
C) [He]
D) [Ne]2s22p6
E) [Ne]

9. Electron Configurations: Exceptions
Half filled and full filled orbitals are more stable. To get d orbitals to this stability promote electrons from s orbitals. ONLY ONE
Fs also have a bunch of exceptions, don’t worry about these. If I ask for an electron configuration from the F block, just follow the rules
Question: Why can we be so fluid with our exchange of electrons from the s and d orbitals?
Energy levels are very close to each other!
There are some situations that arise that don’t follow this typical pattern of filling from low to high, and removing from the highest level. Here I have them listed out, and we’ll go into each in more detail in the following slides.
The first we’ll talk about involves making positive ions. When you are in the d block, you will always remove from the s orbitals first.
Secondly, due to the fact that half filled and fully filled energy levels are more stable, if one electron can be moved up from the s orbital to the d orbital than it will be promoted.
The F orbitals have a bunch of exceptions, but these aren’t as systematic so we won’t worry about them in this class. If you are interested you can refer to the book or internet to see where these are.
Now lets think about why we are able to be so fluid with these electrons. The s and d orbitals are very close to each other and have very similar energy levels. Because of this the slightly higher energy levels of the d orbital, are made up for by the added stability of a half or fully filled energy shell.

10. Is this actually important? (cough cough will you test us on this?)
Absopositivilutely
I promise to put some exceptions (likely at least two) on the exam
that you have to give me the electron configuration for.

11. What is the electron Configuration for neutral chromium
More than one answer may be possible
A) [Ar]4s23d4
B) [Ar]4s14p5
C) [Ar]4s04d5
D) [Ar]4s13d5
E) None of the above.

12. What is the electron Configuration for zinc
More than one answer may be possible
A) [Ar]4s23d10
B) [Ar]4s04p10
C) [Ar]4s24d8
D) [Ar]4s13d9

13. Electron Configurations: Exceptions
When valence d orbitals have electrons and you need to make an positive ion, remove from valence s orbitals first.
There are some situations that arise that don’t follow this typical pattern of filling from low to high, and removing from the highest level. Here I have them listed out, and we’ll go into each in more detail in the following slides.
The first we’ll talk about involves making positive ions. When you are in the d block, you will always remove from the s orbitals first.
Secondly, due to the fact that half filled and fully filled energy levels are more stable, if one electron can be moved up from the s orbital to the d orbital than it will be promoted.
The F orbitals have a bunch of exceptions, but these aren’t as systematic so we won’t worry about them in this class. If you are interested you can refer to the book or internet to see where these are.
Now lets think about why we are able to be so fluid with these electrons. The s and d orbitals are very close to each other and have very similar energy levels. Because of this the slightly higher energy levels of the d orbital, are made up for by the added stability of a half or fully filled energy shell.

14. What is the electron Configuration for Co2+
A) [Ar]4s23d5
B) [Ar]4s04p7
C) [Ar]4s14d6
D) [Ar]4s23d7