Question

What is the formula of aluminum oxide if the formula of aluminum chloride is $\left({\mathrm{AlCl}}_3\right)$.

Answer 1

• The formula of any compound describes the number of atoms present in that compound.
• The formula of any compound is written by combining it's cation and anion valency.

The formula of Aluminium chloride is $\left({\mathrm{AlCl}}_3\right)$.

In Aluminum chloride $\left({\mathrm{AlCl}}_3\right)$, Aluminium ion is written as ${\left(\mathrm{Al}\right)}^{3+}$ and Chloride is written as ${\left(\mathrm{Cl}\right)}^{-}$

• Determination of the formula of Aluminum oxide:

The valency of oxide can be calculated as :

In the case of non-metals, the valency is calculated as:

$\begin{array}{rcl}\mathrm{Valency}& =& 8-(\mathrm{Number}\mathrm{of}\mathrm{valence}\mathrm{electrons})\\ & =& 8-6\\ & =& 2\end{array}$

Therefore, an oxide is written as ${\mathrm{O}}^{2-}$ , because Oxygen $\left(\mathrm{O}\right)$ is an anion and exists as a diatomic in nature.

The Formula of any compound is written by cross-multiplying it's valency with anion and cation and vice versa.

Therefore, the formula of Aluminum oxide is $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$