Chemical bonding and crystal structure of silicon [duplicate]








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I can understand that in Silicon Crystal a central Silicon atom shares its 4 valance electrons with 4 surrounding silicon atoms. And the chain continues. But then What happens to the outermost such Silicon atoms (in the drawing). They each will have incomplete so called octate.




In a Silicon crystal, outermost Silicon atoms are probably oxidized yielding a monoatomic layer of Oxygen atoms, chemically bound by covalences like in $\ce{SiO\_2}$, by analogy with Aluminium. Silicon and Aluminium are neighbors in the periodic table : they often have similar properties. And it is well known that an extremely thin layer of Aluminium Oxide $\ce{Al\_2O\_3}$ does cover Aluminium foils and pieces. It must be the same for Silicon. 


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