Which Element to Use in Electron Configurations

[Drew Myers 4G]

When doing electron configurations for multi-electron atoms, do we always use the noble gas of the previous line to shorten the configuration? Why can't we use the atom that comes before the atom we're doing the configuration for?

[Sebastian Lee 1L]

Typically you would use the last element with a full shell (typically a noble gas) to shorthand. The problem with using the last element is that it would be confusing when identifying the extra electron in your element. For example, if I was doing the configuration for Ca, it would be weird to say [K] 4s¹ because this would be like saying 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹ 4s¹ (the 4s subshell is split?).

Also this could also be problematic considering the exceptions to normal configurations. For example, Cu is [Ar] 3d¹⁰ 4s¹ but Ni (the element right before) is [Ar] 3d⁸ 4s². Saying [Ni] 3d² 4s^-1 is problematic.

[Kavee Dodampahala 4E]

When writing out electron configurations out, there are 2 formats you can use. The first format is writing it all out, for example the electron configuration for lithium would be writing as 1s2 2s1. The second format is naming the past noble gas before the element and just writing the configuration of the addition electrons from there, this way lithium could be written as [He]2s1.

[faithkim1L]

When shortening the electron configuration to make it easier to sort through, people use the noble gas and write out the last line of the electron configuration. However, you can also just write out the whole thing.

[Aayush Patel 3B]

Unless it asks for the full electron configuration of an element, noble gas configuration is an easier way to write it. The noble gas is used because they have no more room for electrons and are stable.

[ZainAlrawi_1J]

As far as this class is concerned, always use the noble gas configuration when applicable unless otherwise indicated. It saves a lot of time and is definitely the "proper" way of doing it.