# How do you determine the formula for aluminium hydroxide?

Dec 13, 2016

"Criss-cross" the charges of each atom because it is an ionic compound. This will get you $A l {\left(O H\right)}_{\text{3}}$.

#### Explanation:

Aluminum has a chemical symbol of $A l$, with a charge of 3+.
Hydroxide is a molecule consisting of two elements - hydrogen and oxygen. The chemical formula for hydroxide is $O {H}^{1 -}$.

Aluminum is the cation, while hydroxide is the anion, thus we get $A l {\left(O H\right)}_{\text{3}}$. This is because we still "criss-cross" the charges as it is an ionic compound - electrons are transferred - so aluminum's charge of 3+ goes to hydroxide while its charge of 1- goes to aluminum.

The 1 is redundant so we don't write it in.

Hope this helps :)