d block before s block

[Viviana Velasquez]

Can somebody explain why you would put 3d^6 4s^2 instead of the other way around?

[Kavya Immadisetty 2B]

Some people write the d-block before the s-block because when an element is losing electrons, it'll lose them from the s-block first. However, my TA said that it's more common for people to write the s-block before the d-block because when electrons are being placed into an element, electrons are added to the s-block and then the d-block.

[Veronica_Lubera_2A]

What also helps me remember that the d block comes before the s block in the electron configuration is that the leading coefficients of d and the blocks before it are the same. For example, 3s2, 3p6, 3d10 (3 is the same) and afterwards, the 4th shell begins.

[Brynne Burrows 3K]

I think this partly has to do with an electron being removed from 4s before it would be removed from 3d. The energy level is lower in the 3d shell, so it would come before 4s when 4s has both electrons.