# Chemical bonding and crystal structure of silicon [duplicate]

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.