## Exceptions to Orbital Rules

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ashwathinair
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Joined: Sat Aug 17, 2019 12:17 am

### Exceptions to Orbital Rules

What are the exceptions to the orbital rules we went over in class? I vaguely remember that d5 and d10 have different energy values so their orbital sequences are different.

Elena Bell 1C
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Joined: Thu Jul 11, 2019 12:16 am

### Re: Exceptions to Orbital Rules

The exceptions we learned is class was the d5 and d10. We learned that these energy states are more stable than their previous states of d4 and d9. Normally, the energy level would increase in numeric order but because atoms like to be stable, the electrons go to the d5 or d10 level instead of the d4 or d9. The extra electron is then "taken" the s orbital. For example, we write Cr as [Ar]3d^54s^1 instead of [Ar]3d^44s^2.

Adrianh72
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Joined: Sat Aug 17, 2019 12:16 am

### Re: Exceptions to Orbital Rules

Since Dr. Lavelle said we only needed to know the first row of the d-block, Chromium (Cr) and Copper (Cu) are the only exceptions we need to know. And this is because they are d5 and d10, respectively.

Christine Honda 2I
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Joined: Sat Sep 14, 2019 12:17 am

### Re: Exceptions to Orbital Rules

The two main exceptions are Chromium ([Ar]3d^5 4s^1) and Copper ([Ar] 3d^10 4s^1)

These are exceptions to the general rule because a completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital. It is easier for them to remove a 4s electron and bring it to the 3d subshell, which will give them a half-filled or completely filled subshell, creating more stability.
Off of the general pattern we would expect the electron config for copper to be [Ar]3d^9 4s^2 but the element is more stable by having the 3d orbital full than the 4s so that's why the electron config is [Ar]3d^10 4s^1

Jiyoon_Hwang_2I
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Joined: Sat Sep 14, 2019 12:17 am

### Re: Exceptions to Orbital Rules

The first exception was that a half full d^5 and full d^10 subshell have lower energy. So, for chromium the electron configuration would be [Ar] 3d^5 4s^1 and the electron configuration of copper would be [Ar] 3d^10 4s^1.

The other exception was that the 4d state has lower energy than the 5s state, after 2 electrons have occupied the 5s state (as shown in period 5 on the periodic table)

Julie Park 1G
Posts: 100
Joined: Thu Jul 25, 2019 12:15 am

### Re: Exceptions to Orbital Rules

For Cu, instead of writing:
Cu: [Ar] 3d^9 4s^2
You would write:
Cu: [Ar] 3d^10 4s^1

This is simply because the latter version presents a more stable electron configuration where the d subshell remains completely full

I believe the two exceptions are that half full d5 and full d10 subshells have lower energies

quresh3E
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Joined: Wed Sep 18, 2019 12:17 am

### Re: Exceptions to Orbital Rules

What does that mean when he said they were half shell and full shell?

Lauren Stack 1C
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Joined: Sat Aug 17, 2019 12:18 am

### Re: Exceptions to Orbital Rules

The exceptions to the expected electron configurations come with Chromium and Copper. Chromium’s electron configuration is [Ar] 3d^5 4s^1. Copper’s is [Ar] 3d^10 4s^1.
As for what half filled and full subshells mean, a d subshell can have up to 10 electrons in it, and half-full would be 5 electrons in that d subshell, and full would mean 10. The reason for the irregularities is that a half-full or full subshell is considerably more stable than other configurations and thus impacts the energy level filling.

Jamie Hwang 2F
Posts: 104
Joined: Thu Jul 25, 2019 12:16 am

### Re: Exceptions to Orbital Rules

quresh3E wrote:What does that mean when he said they were half shell and full shell?

Half shell means when all the orbitals in the subshell have one electron. Full shell means when all the orbitals in the subshell have two electrons. So 3d^5 would be half shell and 3d^10 would be full shell.

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