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In chrysoberyl, a compound containing beryllium, aluminium and oxygen, oxide ions form cubic close packed structure. Aluminium ions occupy $\frac{1}{4}$ th of octahedral voids. The formula of the compound is
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Verified Answer
The correct answer is:
$\mathrm{BeAl}_{2} \mathrm{O}_{4}$
Given, chrysoberyl forms ccp structure.
Oxygen occupies lattice points $=N$ (say)
Al occupies $\frac{1}{2}$ of octahedral voids $=\frac{N}{2}$
Be occupies $\frac{1}{8}$ of tetrahedral voids $=\frac{2 N}{8}$
$\therefore$ The formula of compound is
$\begin{aligned}
&\mathrm{Be}: \mathrm{Al}: \mathrm{O} \\
&\frac{2 N}{8}: \frac{N}{2}: N \\
&\Rightarrow \quad \mathrm{BeAl}_{2} \mathrm{O}_{4}
\end{aligned}$
Oxygen occupies lattice points $=N$ (say)
Al occupies $\frac{1}{2}$ of octahedral voids $=\frac{N}{2}$
Be occupies $\frac{1}{8}$ of tetrahedral voids $=\frac{2 N}{8}$
$\therefore$ The formula of compound is
$\begin{aligned}
&\mathrm{Be}: \mathrm{Al}: \mathrm{O} \\
&\frac{2 N}{8}: \frac{N}{2}: N \\
&\Rightarrow \quad \mathrm{BeAl}_{2} \mathrm{O}_{4}
\end{aligned}$
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