In water solutions the solvated proton H⁺ forms H₃O⁺. So, this is a water molecule with an extra proton attached to give a +1 positive charge.

Ions are compounds that have a net charge. Cations have a positive charge which means that they have more protons (positively charged subatomic particles) than electrons (negatively charged subatomic particles). Anions have a negative charge meaning that they have more electrons than protons. Hydrogen has one proton and one electron resulting in an overall neutral (zero) charge (+1 + -1 =0). Hydrogen can lose an electron to become a +1 charged cation (+1 + 0 = +1) which in the case of hydrogen 1 (the predominant hydrogen isotope) this H+ cation is just a proton. H+ cations are responsible for the pH of a water solution (pH is a measure of acidity). Hydrogen can also gain an electron to become an anion. This H- anion is known as hydride and has one proton and two electrons (+1 + 2^-1= -1). Hydride ions can be important in several organic chemical reactions and is commonly used as a reducing agent (reducing agents are compounds which give one or more electrons to another compound to decrease the second compound's over all charge. When this happens, the second compound is said to have been reduced by the first compound which is known as the reducing agent.)

The most common isotope of hydrogen has one proton and no neutrons, so ionizing it (stripping away the electron) leaves only a proton behind.

Hydrogen can form a cation, with a +1 charge.