S-orbital and D-orbital

[Jaifreen_Bhangu_3K]

When writing electron configurations why is it more favorable to fill the d-orbital instead of the s-orbital?

[Arshiya]

As the number of orbitals increases, the s and d orbitals become very close in energy with s being slightly lower than d. Therefore, the 4s orbital will fill up first and then the 3d orbital will be filled. However, d becomes favorable when the electron has an uneven amount of electrons. Orbitals like to be either half filled or fully filled in order for the element to be more stable. So, d becomes favorable under those circumstances. For example, Nickel has an electron configuration of [Ar]4s2,3d8. However, in order for the electrons to be more stable a [Ar]3d10 configuration is preferred.

[taywebb]

Would the configuration of Ni as [Ar]3d84s2 be considered wrong on a test? Is it always preferred to fill the shell in order to make it more stable?