So when it comes to electron orbital stability, you just need to remember that d subshell orbitals are most stable when they are half-filled or totally filled with electrons because of symmetry. So what we mean by half-filled, remember, we're going to follow Hund's rule, which says that n orbitals that have the same energy that are degenerate are first half-filled. So we're dealing with up, up, up, up, up. Here we have a set of d orbitals electrons that are all facing up. So this set of orbitals are half-filled. Now, totally filled, we go up, up, up, up, up, then come back around, down, down, down, down, down. So here we have an example of a half-filled set of d orbitals, and here a set of totally filled in d orbitals.
The Electron Configuration: Exceptions (Simplified) - Online Tutor, Practice Problems & Exam Prep
Most Electron Configuration Exceptions are the result of elements drive to obtain half filled or totally filled d orbitals.
Electron Configuration Exceptions
The Electron Configuration: Exceptions (Simplified) Concept 1
Video transcript
p and d subshells are most stable when either half filled or totally filled with electrons.
The Electron Configuration: Exceptions (Simplified) Concept 2
Video transcript
Now when looking at exceptions to the electron configurations, we're going to say starting from chromium, which is Cr, as the atomic number z increases, exceptions to electron configurations can be observed. A memory tool here we can have is that chromium has an atomic number of 24. So think about that, 24. We're going to say that the exceptions happen with these 2 elements and with these 4 elements, so 24. We're going to start out with chromium, we know that's where it starts, and we're going to skip the next 4 columns. Right? So we start out with chromium and you skip the next 4. So skip Manganese, skip Iron, skip Cobalt, skip Nickel, and then you land on copper where the next group of exceptions can exist. So just remember, these are the 6 major types of elements where we're going to see exceptions to the electron configuration. So keep this in mind when we're looking at their electron configurations. Now that we know that these are the 6 to that we have to deal with, let's see how these exceptions arise. So click on the next video and let's see what happened.
The Electron Configuration: Exceptions (Simplified) Concept 3
Video transcript
So remember, exceptions start with chromium. So let's look at chromium. If we were to determine its electron configuration initially, we would see that it would look like argon 4s23d4. Now here, what do we have here? We have 3d4 with four electrons within it. But remember, earlier we said that s and d subshells or sublevels have this urge to try to be half-filled or totally filled. Now we're going to say, an s orbital electron can be promoted to create half-filled orbitals with d4 electrons. So what we're saying here is if you're doing the electron configuration of chromium, you're going to end with a d4. That's a key to tell you that, oh, d4. We have only four electrons within these d orbitals. But if I could somehow get one more electron in there, those d orbitals will be half-filled. So what's going to happen here is we're going to take a d5, and our 4s2 just gave up an electron so it becomes 4s1. So it now looks like this. This would be the correct electron configuration of chromium. So again remember, chromium has this type of exception, and the driving force is trying to get a half-filled set of d orbitals. Okay. So here, we're not going to land we're not going to stay as d4, when it's neutral it's going to become a d5. Now that we've seen this with the first column, let's see what happens with the second column. So click on the next video and let's see what happens with them.
When electron configuration ends with d4, an s orbital electron is promoted to d orbital to create half filled orbital:d5.
The Electron Configuration: Exceptions (Simplified) Concept 4
Video transcript
So if we look at the 2nd column, let's look at copper. Now copper, if we were to look at the periodic table, we'd initially think it's argon s2d9. But if we look at the 3d9 orbitals, what we should notice is we just need one more electron here and it will be completely filled. Remember there's this need, this drive by your p and d sublevels or subshells to be either half-filled or totally filled. So we're going to say here, an electron, an s orbital electron, can be promoted to create completely filled orbitals with d 9 elements. Here copper is a d nine element. It ends with d 9. If you just get one more electron it can become d 10, and that's what's going to happen. We take one from the s orbital, before s orbital, and we donate it over to the d. Doing this now, we only have one electron here within 4s, and this now becomes totally filled in and therefore more stable. So now this is s1d10. So just remember, we have these 6 elements we discussed previously in the videos, they have this drive where we're going to take 1 electron from an s orbital and promote it to 1 of the d orbitals, so that we can create either a half-filled d orbitals or totally filled, completely filled d orbitals. Remember this driving force that causes the exceptions within these neutral elements.
When electron configuration ends with d9, an s orbital electron is promoted to d orbital to create completely filled orbital:d10.
The Electron Configuration: Exceptions (Simplified) Example 1
Video transcript
Here in this example question, it says, based on the exceptions, provide the condensed electron configuration for the silver atom. So we're going to say here that silver is an element. It has an atomic number of 47. Since we're dealing with an atom, it's the neutral form of it, so it has 47 electrons. Now, looking at the periodic table, what we would see initially is we would see krypton 5s24d9. Remember, silver is one of the elements within the second column we discussed, and remember it's a d nine element. If it can become d ten, those orbitals will be completely filled. In order to do this, we're going to take 1 electron from the s orbital and promote it up to the d set of orbitals. Doing this gives us now the correct exception to silver, which is Krypton 5s14d10. So this would be the correct electron configuration for silver. So just keep in mind these six elements we discussed earlier, all of them do this, where we take 1 electron from the s orbital and promote it up, so that we either have half-filled d orbitals or completely filled in d orbitals like silver here.
Illustrate the exception to the electron configuration of molybdenum.
Problem Transcript
Which of the following is the correct electron configuration of gold?
A comparison of the electron configurations of palladium (Pd) and silver (Ag) indicates that: