What is "hydron"

n. (context chemistry English) any hydrogen cation

In chemistry, a hydron is the general name for a cationic form of atomic hydrogen, represented with the symbol . However, in most textbooks, this term is avoided and instead " proton" is used, which strictly speaking refers to the cation of protium, the most common isotope of hydrogen. The term "hydron" includes cations of hydrogen regardless of their isotopic composition: thus it refers collectively to protons (H) for the protium isotope, deuterons (H or D) for the deuterium isotope, and tritons (H or T) for the tritium isotope. Unlike other ions, the hydron consists only of a bare atomic nucleus.

The hydron (a completely free or "naked" hydrogen atomic nucleus) is too reactive to occur in many liquids, even though it is sometimes visualized to do so by students of chemistry. A free hydron would react with a molecule of the liquid to form a more complicated cation. Examples are the hydronium ion in water-based acids, and , the unstable cation of fluoroantimonic acid, the strongest superacid. For this reason, in such liquids including liquid acids, hydrons diffuse by contact from one complex cation to another, via the Grotthuss mechanism.

The hydrated form of the hydrogen cation, the hydronium (hydroxonium) ion (aq), is a key object of Arrhenius' definition of acid. Other hydrated forms, the Zundel cation which is formed from a proton and two water molecules, and the Eigen cation , a hydronium ion and three water molecules, play an important role in "hydron hopping" according to the Grotthuss mechanism. The hydron itself is crucial in more general Brønsted–Lowry acid–base theory, which extends the concept of acid–base chemistry beyond aqueous solutions.

The negatively charged counterpart of the hydron is the hydride anion, .

Hydron has the following meanings:

• Hydron (chemistry), a positive hydrogen cation
• Hydron (He-Man), a character in the He-Man universe
• Hydron (medicine), a Chinese brand of eye drops for lenses