Hydrogen ion

Hydrogen ion is recommended by IUPAC as a general term for all ions of hydrogen and its isotopes. Depending on the charge of the ion, two different classes can be distinguished: positively charged ions and negatively charged ions.

Under aqueous conditions found in biochemistry, hydrogen ions exist as the hydrated form hydronium, H3O+, but these are often still referred to as "hydrogen ions" or even "protons" by biochemists.

Cation (positively charged)
When hydrogen loses its electron, the following cations can be formed:

In addition, the ions produced by the reaction of these cations with water as well as their hydrates are called hydrogen ions:
 * Hydron: general name referring to the positive ion of any hydrogen isotope (H+)
 * Proton: 1H+ (most correctly, the cation of protium)
 * Deuteron: 2H+, D+
 * Triton: 3H+, T+


 * Hydronium ion: H3O+
 * Zundel cation: H5O2+ (named for Georg Zundel)
 * Eigen cation: H9O4+ (named for Manfred Eigen)

Zundel cations and Eigen cations play an important role in proton hopping according to the Grotthuss mechanism.

In connection with acids, hydrogen ions typically refer to hydrons.

Anion (negatively charged)
Hydrogen anions are formed when additional electrons are acquired:


 * Hydride: general name referring to the negative ion of any hydrogen isotope (H&minus;)
 * Deuteride: 2H&minus;, D&minus;
 * Tritide: 3H&minus;, T&minus;