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

Aluminum is on the third column after the previous noble gas (##"Ne"##). In order to achieve a full valence shell, it can lose ##3## to become ##"Al"^(3+)##.

In return, it wants neutrality. Each ##"OH"^(-)## contributes a ##-1## charge, so to balance out a ##+3## charge, you need ##3xx"OH"^(-)##.

So, the product of the following combination is aluminum hydroxide:

##"Al"^(3+) + 3"OH"^(-) -> bb("Al"("OH")_3)##

Note how the charges balance out. ##+3 + (3xx -1) = 0##.