## Valence Electrons and Electron Configuration

JamieVu_2C
Posts: 108
Joined: Thu Jul 25, 2019 12:16 am

### Valence Electrons and Electron Configuration

If you're forming an ion from an atom that has its d-orbitals filled, then are the d-orbitals still considered valence electrons? For example, the electron configuration of Ga is [Ar] 3d^10 4s^2 4p^1. But if you want to form the Ga ion, you would only remove the electrons in the 4s and 4p orbitals to make the ion Ga^3+ with the electron configuration of [Ar] 3d^10. Does this mean that the valence electrons are only from the 4s and 4p orbitals and not the 3d orbitals?

Also, as a follow up question, if this is true, then does it only apply to half-filled or full d-orbitals, or does it also to apply to partially filled d-orbitals as well, like for Cr: [Ar]3d^4 4s^2. Would Cr then have 6 valence electrons?

JasonLiu_2J
Posts: 109
Joined: Sat Aug 24, 2019 12:17 am

### Re: Valence Electrons and Electron Configuration

I believe that when counting valence electrons in an atom, you only consider those in the outermost shell/energy level. In Ga for example, since it only has 3 electrons in its 4s and 4p orbitals, it would only have 3 valence electrons. The 3d electrons are part of the n=3 energy level, and would not be counted as valence electrons. As another example, Xe only has 8 valence electrons, despite also have a full 4d subshell, since it only takes into account the electrons in the 5s and 5p orbitals (those in the same shell). This rule would apply no matter the number of electrons in the d subshell, since these electrons would always be on a lower energy level than the s and p electrons for the element in question. Thus, from your example, Cr, which has the electron configuration of [Ar] 3d5 4s1 (remember that this is an exception to the electron configuration rules) would have one valence electron from its 4s orbital. Hope this helps!