## Valence Electron

Brice McKeown 3D
Posts: 35
Joined: Fri Sep 28, 2018 12:25 am

### Valence Electron

I have a question on the problem 2A.1 from the seventh edition... why when asked to give the number of valence electrons (including d electrons) does Sb have 5 valence electrons when it has 10 electrons in the 4d shell.... and then Mn has 7 and you include its d block electrons? Why do some include d block electrons but not others?

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Joined: Fri Sep 28, 2018 12:16 am
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### Re: Valence Electron

The electron configuration for Sb is [Kr]4d105s25p3. The valence electrons are the electrons in the outermost shell. In the case, the outermost shell is n=5. Thus, the valence electrons are the five electrons in 5s and 5p.

Since 4d is completely filled in Sb they are not valence electrons. 3d is not completely filled in Mn while 4s is, so the valence electrons in Mn come from both 3d and 4s, adding up to 7 valence electrons.

Posts: 31
Joined: Fri Sep 28, 2018 12:28 am

### Re: Valence Electron

The big concept behind valence electrons are that they are ones in the orbitals furthest out and unfilled. 5s^2 and 5p^3 are not filled orbitals and therefore the number of valence electrons for the element Sb = 5.

For Mn, the electron configuration would be [Ar]3d^5 4s^2. In this case as Venya said, since the 3d and the 4s orbitals are not filled, and therefor the amount of valence electrons is the combination of electrons in both of these orbitals.