# Aluminum hydroxide is a popular antacid. What is the formula of aluminum hydroxide?

Aluminum is on the third column after the previous noble gas ($\text{Ne}$). In order to achieve a full valence shell, it can lose $3$ valence electrons to become ${\text{Al}}^{3 +}$.
In return, it wants neutrality. Each ${\text{OH}}^{-}$ contributes a $- 1$ charge, so to balance out a $+ 3$ charge, you need $3 \times {\text{OH}}^{-}$.
"Al"^(3+) + 3"OH"^(-) -> bb("Al"("OH")_3)
Note how the charges balance out. $+ 3 + \left(3 \times - 1\right) = 0$.