A hydroxide ion is made up of one oxygen atom and one hydrogen atom, bonded together with a single covalent bond. However, it carries a negative charge (-1).

Here's how to understand this:

* Oxygen typically has 6 electrons in its outer shell, and it wants 8 to be stable.

* Hydrogen typically has 1 electron in its outer shell and wants 2 to be stable.

* When they bond, they share electrons, but the oxygen atom ends up with one more electron than it needs.

* This extra electron gives the hydroxide ion its negative charge.

So, the hydroxide ion can be represented as OH⁻.