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Silicon used in computer chips must have an impurity level below $10^{-9}$ (that is, fewer than one impurity atom for every $10^9 \mathrm{Si}$ atoms). Silicon is prepared by the reduction of quartz $\left(\mathrm{SiO}_2\right)$ with coke (a form of carbon made by the destructive distillation of coal) at about $2000^{\circ} \mathrm{C}$ :

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

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

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

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

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

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

Solution

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

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