In chemistry, the hydron, informally called proton,[2] is the cationic form of atomic hydrogen, represented with the symbol H+.

Other things being equal, compounds that readily donate hydrons (Brønsted acids, see below) are generally polar, hydrophilic solutes and are often soluble in solvents with high relative static permittivity (dielectric constants).

The unsolvated hydron (a completely free or "naked" hydrogen atomic nucleus) does not exist in the condensed (liquid or solid) phase.

As the surface Electric field strength is inverse to the radius, a tiny nucleus interacts thousands times stronger with nearby electrons than any partly ionized atom.

For this reason, in liquid strong acids, hydrons are believed to diffuse by sequential transfer from one molecule to the next along a network of hydrogen bonds through what is known as the Grotthuss mechanism.

Although the ion H3O+(aq) is often shown in introductory textbooks to emphasize that the hydron is never present as an unsolvated species in aqueous solution, it is somewhat misleading, as it oversimplifies infamously complex speciation of the solvated proton in water; the notation H+(aq) is often preferred, since it conveys aqueous solvation while remaining noncommittal with respect to the number of water molecules involved.