Electron Configurations of Transition Metals: Exceptions - Online Tutor, Practice Problems & Exam Prep

Transition metals exhibit exceptions in electron configurations, particularly in chromium (Cr) and palladium (Pd). For Cr (atomic number 24), the expected configuration is altered from ${\mathrm{Ar}}^4{s}^2{d}^4$ to ${\mathrm{Ar}}^4{s}^1{d}^5$ due to electron promotion. Similarly, in period 5, elements like niobium (Nb) also show this behavior, with configurations adjusted to ${\mathrm{Kr}}^5{s}^1{d}^4$. Understanding these exceptions is crucial for mastering transition metal chemistry.

Exceptions (I)

In this video, we're going to take a look at the first type of exceptions that exist for certain transition metals. Here we're going to say starting from chromium. So chromium is right here. As the atomic number Z increases, exceptions to electron configurations can be observed. So our memory tool here is that chromium has an atomic number of 24, and there are two and four. So we have these two elements that have this type of exception, version one, and then these four here O to get the other column.

Remember to skip next 4. All right, so here we're going to say 2. So we're starting with Chromium, and then we skip the next 4. And then here goes our group of four. Now all of these elements have our shell number N and all of them have one electron in their S orbital, so those will be N South to the one. If we take a look here, we're going to say an S orbital electron can be promoted to create half filled orbitals with D₄ and D₉ elements.

So if we were to look at the electron configurations of these, these would be D₄ initially and these would be D₉ initially before the promotion of an electron from the S orbital. So for example, if we took a look at chromium, chromium has an atomic number of 24. We would think that its electron configuration is argon 4S²3D⁴. But again, since it's an exception one type transition metal, one of the electrons from the S orbital would get promoted over to our D.

So now its electron orbital diagram would look like one in the 4S and five electrons in the 3D orbitals, giving us a new electron configuration of argon 4S¹3D⁵. Just remember when it comes to these elements in particular they fit under exception one, they are D₄ and D₉ elements. But because of the promotion of an electron from the South orbital, we change the D₄s into D₅ as we see here and D₉s would become D₁₀s all right. So just remember these particular elements under this first type of exception.

Electron Configurations Of Transition Metals: Exceptions Example

Here it says write the condensed electron configuration of the following ion. So here we have to do it for the silver ion. Its atomic number is 47, neutral silver if we look at the periodic table would look like it's initially Krypton 5 S₂ 4 D₉. But remember it's one of the elements that exists under exception one. We would take an electron from an S orbital and promote it to the D. So the real electron configuration of neutral silver would be Krypton 5 S₁ 4 D₁₀.

So we're looking at this as the real electron configuration of neutral silver. Now plus one means we've lost one electron which is going to come from the highest shell number. Here this one electron is in the 5th shell and these ten are in the fourth shell. The one electron we need to lose would come from the 5th shell.

So here it's electron. Condensed electron configuration would be Krypton 4 D₁₀ and the way it would look is it would be Krypton. Our five is gone now so that orbital would not be filled in. These five would represent our 4D orbitals and be up, up, up, up, up and then come back, around, down, down, down, down, down. So here we have our condensed electron configuration and our electron orbital diagram.

Provide a condensed electron configuration for Au atom and Au (III) ion.

• A. Au: [Xe]6s²4f¹⁴5d⁹
  Au³⁺: [Xe]6s²4f¹⁴5d⁶
• B. Au: [Xe]6s²4f¹⁴5d¹⁰
  Au³⁺: [Xe]4f¹⁴5d⁹
• C. Au: [Xe]6s¹4f¹⁴5d¹⁰
  Au³⁺: [Xe]4f¹⁴5d⁸
• D. Au: [Xe]6s¹4f¹⁴5d¹⁰
  Au³⁺: [Xe]6s¹4f¹⁴5d⁷

Exceptions (II)

In this video we take a look at exception type 2's that we have. We're going to say additional exceptions to the electron configuration are observed in. 5 or row five of the periodic table, and a memory tool to help us recall which one they are is 5/8 the number 8B. So if we take a look here, we're dealing with five S group 5B and eight, eight, so 8B.

So looking at these four elements in particular, now we're going to say all are going to have one electron in their 5S orbital. But notice that Palladium is in a different color. That's because Palladium is different from the other three, so it has its own exception on top of the others. For Palladium, we're going to say Palladium has zero electrons in its 5S orbital.

Now if we take a look here, we're going to say that for these elements in particular, the 5S orbital electron or electron is are promoted to a 4D orbital. NB here is niobium. Its atomic number is 41. Its initial electron configuration looks like it would be Krypton 5 S 24 3, but again it's one of the ones in blue and they must have one electron in their S orbital.

So that would mean that we promote this electron to our D orbital. So the new electron configuration would actually be 51 44. Filling U our electron orbital diagram we'd have one electron in the 5S orbital and then following hunts rule we'd half fill to put in our four electrons that are in our 4D orbitals. So this would represent the real electron configuration of niobium. So just remember these are exceptions to for these particular transition metals.

Electron Configurations Of Transition Metals: Exceptions Example

Here it says provide a condensed electron configuration for Ruthenium atom. So atom means its neutral form. If we look at the periodic table, it would look like Ruthenium is Krypton 5S²4D⁶. But remember it's one of our exception twos.

In it we can only have one electron in our S orbital, so one of these electrons gets promoted to our 4D orbital. So the real electron configuration of ruthenium is Krypton 5S¹4D⁷. This will be our final answer for the condensed electron configuration of this particular transition metal atom.

Given the following electron configuration, determine the identity of ion with +2 charge.

• A. Pd²⁺
• B. Ru²⁺
• C. Pb²⁺
• D. Cd²⁺

Here’s what students ask on this topic:

What are the exceptions to the electron configurations of transition metals?

Exceptions to the electron configurations of transition metals occur primarily in two types. Exception type 1 involves elements starting from chromium (atomic number 24) and follows a pattern of '2, skip, next 4'. In these elements, an electron from the s orbital is promoted to the d orbital, changing configurations like d₄ to d₅ and d₉ to d₁₀. For example, chromium's configuration changes from [Ar] 4s² 3d⁴ to [Ar] 4s¹ 3d⁵. Exception type 2 is observed in period 5, specifically in group 5b and 8b, affecting elements like Niobium. These elements generally have one electron in their 5s orbital, except for palladium, which has none. Niobium's configuration changes from [Kr] 5s² 4d³ to [Kr] 5s¹ 4d⁴ due to electron promotion.

Why does chromium have an unusual electron configuration?

Chromium has an unusual electron configuration because it falls under exception type 1 for transition metals. Normally, we would expect chromium to have the electron configuration [Ar] 4s² 3d⁴. However, to achieve a more stable configuration, one electron from the 4s orbital is promoted to the 3d orbital, resulting in [Ar] 4s¹ 3d⁵. This configuration allows for half-filled d orbitals, which are more stable due to reduced electron-electron repulsion and increased exchange energy.

What is the electron configuration of Niobium and why is it an exception?

Niobium (Nb) has an atomic number of 41 and falls under exception type 2 for transition metals. Its expected electron configuration is [Kr] 5s² 4d³. However, due to the promotion of an electron from the 5s orbital to the 4d orbital, its actual electron configuration is [Kr] 5s¹ 4d⁴. This promotion occurs to achieve a more stable configuration with a half-filled d orbital, which reduces electron-electron repulsion and increases exchange energy.

How does the electron configuration of palladium differ from other transition metals in period 5?

Palladium (Pd) is unique among transition metals in period 5 because it has no electrons in its 5s orbital. While other elements in this period typically have one electron in their 5s orbital, palladium's electron configuration is [Kr] 4d¹⁰. This configuration is achieved by promoting both 5s electrons to the 4d orbital, resulting in a fully filled d orbital, which is highly stable due to minimized electron-electron repulsion and maximized exchange energy.

What is the significance of half-filled and fully filled d orbitals in transition metals?

Half-filled and fully filled d orbitals in transition metals are significant because they provide extra stability to the atom. This stability arises from reduced electron-electron repulsion and increased exchange energy. For example, in chromium, the promotion of an electron from the 4s to the 3d orbital results in a half-filled 3d⁵ configuration, which is more stable than a partially filled d⁴ configuration. Similarly, a fully filled d¹⁰ configuration, as seen in palladium, is highly stable due to the symmetrical distribution of electrons.