"Exception" in Writing Electron Configurations

claudia_1h
Posts: 111
Joined: Fri Aug 09, 2019 12:16 am

"Exception" in Writing Electron Configurations

In class today, Dr. Lavelle discussed an "exception" in writing electron configurations... He said "Half full d5 and full d10 subshells have lower energy". So in the example of Cr, the configuration is written as [Ar]3d5 4s1. Can anyone explain this to me? Why does the 4s shell not get filled first?

KMenjivar_3A
Posts: 25
Joined: Mon Jan 07, 2019 8:05 am

Re: "Exception" in Writing Electron Configurations

By following these certain exceptions when it comes to writing electron configurations, these half filled shells are exhibited to be more symmetry and more stable.

Sanjana Munagala_1j
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Joined: Sat Aug 24, 2019 12:17 am
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Re: "Exception" in Writing Electron Configurations

When writing electron configurations, you want to describe where electrons would be located when they are in their ground state or exhibit the lowest energy. In these two exceptions, having a half full or a full d-subshell is more stable than having a full s-subshell, which also makes sense, since in these elements, the 3d orbitals have a lower energy than the 4s orbitals.

Hope that helps!

Lindsey Chheng 1E
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

Re: "Exception" in Writing Electron Configurations

claudia_1e wrote:In class today, Dr. Lavelle discussed an "exception" in writing electron configurations... He said "Half full d5 and full d10 subshells have lower energy". So in the example of Cr, the configuration is written as [Ar]3d5 4s1. Can anyone explain this to me? Why does the 4s shell not get filled first?

-The exceptions for Electron Configurations are for certain Transition Metals.
A. This phenomenon is prevalent in atoms with d and f electrons
B. Examples:
1. Cr (Mo, too): [Ar} 4s^2 3d^4 is actually [Ar]4s^1 3d^5
2. Cu (Ag, Au too): [Ar]4s^2 3d^9 is actually [Ar]4s^1 3d^10
3. The reason this occurs is that these configurations are energetically favorable. This means that they have a lower energy.
C. This occurs for Cr, Mo, Cu, Ag, Au when these elements are neutral.
-Most s and p block elements become ions that have noble gas configurations
A. Example:
1. N: 1s^2 2s^2 2p^3 N^3-: 1s^2 2s^2 2p^6 , which is isoelectronic to Ne
-For transition metals, the outer s electrons are lost first because it takes too much energy to pull off all the s and d electrons. Therefore, when writing the electron configurations, always pull of the s first! Remember: every element has all energy levels, it just depends whether it's occupied or not.
A. Example:
1. Mn^2+
Mn: [Ar}4s^2 3d^5 so Mn^2+ is [Ar]3d^5

Anvi Brahmbhatt 4A
Posts: 51
Joined: Wed Sep 18, 2019 12:21 am

Re: "Exception" in Writing Electron Configurations

Lindsey Chheng 1H wrote:
claudia_1e wrote:In class today, Dr. Lavelle discussed an "exception" in writing electron configurations... He said "Half full d5 and full d10 subshells have lower energy". So in the example of Cr, the configuration is written as [Ar]3d5 4s1. Can anyone explain this to me? Why does the 4s shell not get filled first?

-The exceptions for Electron Configurations are for certain Transition Metals.
A. This phenomenon is prevalent in atoms with d and f electrons
B. Examples:
1. Cr (Mo, too): [Ar} 4s^2 3d^4 is actually [Ar]4s^1 3d^5
2. Cu (Ag, Au too): [Ar]4s^2 3d^9 is actually [Ar]4s^1 3d^10
3. The reason this occurs is that these configurations are energetically favorable. This means that they have a lower energy.
C. This occurs for Cr, Mo, Cu, Ag, Au when these elements are neutral.
-Most s and p block elements become ions that have noble gas configurations
A. Example:
1. N: 1s^2 2s^2 2p^3 N^3-: 1s^2 2s^2 2p^6 , which is isoelectronic to Ne
-For transition metals, the outer s electrons are lost first because it takes too much energy to pull off all the s and d electrons. Therefore, when writing the electron configurations, always pull of the s first! Remember: every element has all energy levels, it just depends whether it's occupied or not.
A. Example:
1. Mn^2+
Mn: [Ar}4s^2 3d^5 so Mn^2+ is [Ar]3d^5

Thank you so much for the thorough explanation as I was also confused. It was very helpful!