## Valence Electrons

Orly Termeie 3I
Posts: 94
Joined: Fri Sep 25, 2015 3:00 am

### Valence Electrons

Hello! The number of valence electrons a element has is determined by the number of electrons in shells that are not full, correct? For instance Nickel has 10 valence electrons while Gallium has 3 correct? Also, how would you determine the valence electron configuration for these elements?
Thanks!

Chloe 3D
Posts: 21
Joined: Fri Sep 25, 2015 3:00 am

### Re: Valence Electrons

Hello,

You're correct. The number of valence electrons is the number of electrons in the outer shell of an atom. To determine the valence electron configuration of an element, you first select select the nearest noble gas preceding the element. For nickel, this would be argon.

The electron configuration of Ni can thus be expressed as that of Ar plus 10 valence electrons. Because the 4s orbital is lower in energy than the 3d orbital, Ni's first two valence electrons can be placed in the 4s orbital. The remaining 8 electrons are placed in the 3d orbital. Remember that after the first electron is added, though, the 3d orbital becomes lower in energy than the 4s.

So, the electron configuration of Ni can be stated as [Ar]3d^84s^2.

Hannah Markovic 3C
Posts: 32
Joined: Fri Sep 25, 2015 3:00 am

### Re: Valence Electrons

The first reply is not entirely correct. Yes, the number of valence electrons is the number of electrons in the outermost shell and the electron configuration of Ni is [Ar] 3d^8.4s^2. However, this makes the number of valence electrons of Nickel 2, not 10, because the d electrons are in the 3 shell and not the 4 shell. There are only 2 electrons in the 4 shell, so the number of valence electrons for Ni is 2. This is also why Ga has 3 valence electrons because its electron configuration is [Ar] 3d^10.4s^2.4p^1, so the number of electrons in the 4th shell is now 3. Just remember that d orbital electrons are usually not valence electrons and s and p electrons will always be valence electrons.