If 3d is higher in energy than 4S, how is 4s ionised first?

[KingCrimson]

Main Question or Discussion Point

just as the title says, how is 4s ionised first if 3d is higher in energy? also, how does argon have a full outershell if its 3d is empty?

 

[mfb]

Ionized first by which process? You can kick out every electron with sufficient energy. In addition, removing an electron will shift the energy levels for the other electrons.

"Full" in the context of noble gases refers to the s and p orbitals.