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Silicon used in computer chips must have an impurity level below 10910^{-9} (that is, fewer than one impurity atom for every 109Si10^9 \mathrm{Si} atoms). Silicon is prepared by the reduction of quartz (SiO2)\left(\mathrm{SiO}_2\right) with coke (a form of carbon made by the destructive distillation of coal) at about 2000C2000^{\circ} \mathrm{C} :

SiO2( s)+2C(s)Si(l)+2CO(g)\mathrm{SiO}_2(\mathrm{~s})+2 \mathrm{C}(\mathrm{s}) \longrightarrow \mathrm{Si}(l)+2 \mathrm{CO}(\mathrm{g})

Next, solid silicon is separated from other solid impurities by treatment with hydrogen chloride at 350C350^{\circ} \mathrm{C} to form gaseous trichlorosilane (SiCl3H)\left(\mathrm{SiCl}_3 \mathrm{H}\right) :

Si(s)+3HCl(g)SiCl3H(g)+H2( g)\mathrm{Si}(\mathrm{s})+3 \mathrm{HCl}(\mathrm{g}) \longrightarrow \mathrm{SiCl}_3 \mathrm{H}(\mathrm{g})+\mathrm{H}_2(\mathrm{~g})

Finally, ultrapure Si\mathrm{Si} can be obtained by reversing the above reaction at 1000C1000^{\circ} \mathrm{C} :

SiCl3H(g)+H2( g)Si(s)+3HCl(g)\mathrm{SiCl}_3 \mathrm{H}(\mathrm{g})+\mathrm{H}_2(\mathrm{~g}) \longrightarrow \mathrm{Si}(\mathrm{s})+3 \mathrm{HCl}(\mathrm{g})

What types of crystals do Si\mathrm{Si} and SiO2\mathrm{SiO} 2 form?


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The problem asks to identify the type of crystalline solid for elemental silicon and silicon dioxide (quartz).

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