Solid-State Electronics and Devices-Valence electrons

[lmartinel]

Hey guys:

It have been out of college for a while now. I decided to start studying to take my Fundamentals of Engineering (FE) exam. However, I do not remember a lot about Chemistry. I acknowledge this is an electronics Forum but I am sure you guys can help me out with a question on valence electrons. Here goes:

Silicon is the most-used semiconductor in electronic devices. The number of valence electrons in a silicon atom is? Well, the answer is 4 valence electrons.

However, it is not clear to me where it came from. I know that Silicon has an atomic number of 14 and an electronic configuration of 1s^2 2s^2 2p^6 3s^2 3p^2 . I can see that it is willing to loose two electrons but not 4. Can anyone of you elaborate on how to come to a conclusion that indeed 4 valence electrons is the magic number.

I figure I get you guys' mind away, for a second, from your electrical stuff and get back the tiny world of valence electrons. Thank you in advance

 

[user_88]

As I recall, the noble or inert electron shell configuration is 2n².
For the first shell, n=1 and it holds 2 electrons.
For the second shell n=2, so noble configuration is 8.
For n=3, the completely full shell number is 18, but silicon only has 4 outlying electrons, and is therefore not as stable as it would be with the full complement of 18.