# How can silicon have a capacity of 8 electrons in the outer shell?

I was reading an article on how solar cells work in this website- http://science.howstuffworks.com/environmental/energy/solar-cell2.htm In that website I have a doubt in the first paragraph i.e.-
"Silicon has some special chemical properties, especially in its crystalline form. An atom of sili­con has 14 electrons, arranged in three different shells. The first two shells -- which hold two and eight electrons respectively -- are completely full. The outer shell, however, is only half full with just four electrons. A silicon atom will always look for ways to fill up its last shell, and to do this, it will share electrons with four nearby atoms. It's like each atom holds hands with its neighbors, except that in this case, each atom has four hands joined to four neighbors. That's what forms the crystalline structure, and that structure turns out to be important to this type of PV cell."

In that paragraph there is this line that silicon's outer shell has 4 electrons which is half full so it means that its capacity of holding electrons in the outer shell is 8 electrons but according to the $2n^2$ formula silicon's outer shell should have a capacity of holding 18 electrons but why it is not written like that there in the article??

And if its a misprint and i am correct then the whole working of the PV cell in that article should change so whats the correct working??

Regards,
Bhavesh

Thanks.

The filling order of the shells is 1s, 2s, 2p, 3s, 3p, 4s, 3d, ...

Silicon, with 14 electrons, has only filled 1s, 2s, 2p, 3s and half of 3p. It hasn't any electrons in 4s or 3d (in the ground state).

Although the 3rd orbital can have a maximum of 18 electrons, the shell is considered full with 8 electrons if the 4s is not filled.

• The thing you are saying that its considered does not make any sense, can you explain me in a much better way. Till the first 2 shells they follow th $2n^2$ formula and then in the last shell they simply assume somthing, does not make any sense please explain in a much better way. Apr 13 '15 at 3:18
• The superscripts indicate how many electrons are in the shell. Since I am talking about how the shells are filled, there is not a specific number of electrons, the superscripts are not needed. If I stated that the configuration for silicon is $1s^2, 2s^2, 2p^6, 3s^2, 3p^4$, then the superscripts are needed.
– LDC3
Apr 13 '15 at 3:18
• Please see Filling Electrons Shells: en.wikibooks.org/wiki/General_Chemistry/Filling_Electron_Shells
– LDC3
Apr 13 '15 at 3:23