A water molecule with an extra hydrogen atom is called a hydronium ion, represented by the chemical formula H₃O⁺.

Here's why:

* Normal water: A water molecule (H₂O) consists of two hydrogen atoms and one oxygen atom.

* Extra hydrogen: When an extra hydrogen atom attaches to the oxygen atom of a water molecule, it forms a positively charged ion. This ion is called a hydronium ion.

The addition of the extra hydrogen atom creates a positive charge because the hydrogen atom donates its electron to the oxygen atom. This makes the hydronium ion an important component in acid-base chemistry.