Electron Configurations

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Melody Zhang 3L
Posts: 35
Joined: Fri Sep 28, 2018 12:21 am

Electron Configurations

Postby Melody Zhang 3L » Wed Oct 24, 2018 10:48 pm

I understand why we use the noble gases to write the shorthand version of the electron configuration for say the element Chromium, but I'm not sure how we're supposed to know exactly what number to start on after. For example, Chromium is [Ar] 3d5 4s1, but how do we know to start on 3d?

105114680
Posts: 60
Joined: Fri Sep 28, 2018 12:23 am

Re: Electron Configurations

Postby 105114680 » Wed Oct 24, 2018 11:07 pm

The shell n=3 is lower in energy than the shell n=4 and thus it is written first to get the lowest energy configuration. The shells in the configuration should be in order of numerical value (which makes sense because it is in order of increasing energy). Since the d-block is included after Argon, all elements after Ar will have d-block orbitals and/or f-block orbitals that need to be written before the s-block orbitals. This is especially helpful when writing configurations for ions (particularly, cations) so the correct electrons are removed from the configuration. Hope this was helpful!

Sophia_Kiessling_2L
Posts: 61
Joined: Fri Sep 28, 2018 12:26 am

Re: Electron Configurations

Postby Sophia_Kiessling_2L » Wed Oct 24, 2018 11:14 pm

d-block always comes before s-block when the electron configuration is written because it has a lower energy level than the s-block

Sophie Roberts 1E
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

Re: Electron Configurations

Postby Sophie Roberts 1E » Thu Oct 25, 2018 9:03 am

4s would logically come next because it is the shell that is after Argon, however, in this case as we move onto the 3d level, we have to remember that the 3d level is less in energy than the 4s level. Electron configurations are always written in lowest energy to highest energy, so this electron configuration must follow this rule and start with the 3d level (lowest energy) and finish with the 4s level (highest energy).


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