hidrogénion

Hidrogénion is the positively charged hydrogen species that results when a hydrogen atom loses its electron. In many environments a truly free hydrogen ion cannot exist; in aqueous solutions it is highly solvated and is usually described as a hydronium ion, H3O+. The term H+ is often used in chemical equations to represent this solvated proton.

In water, the bare proton is rapidly surrounded by water molecules to form H3O+, and more detailed solvation structures have been proposed, such as the Zundel cation (H(H2O)2+) and the Eigen cation (H9O4+). Proton transfer between water molecules occurs very quickly through hydrogen-bond networks via the Grotthuss mechanism, which underlies fast proton mobility in liquids.

In acid–base chemistry, the hidrogénion is central to defining acidity. Water undergoes autoprotolysis: 2 H2O ⇌ H3O+ + OH−. At 25 °C, the ion product Kw is about 1.0 × 10−14, and the pH of a solution is defined as pH = −log10[H3O+]. Strong acids increase the concentration of H3O+, lowering pH, while bases reduce it.

Aside from aqueous solutions, a bare proton exists in the gas phase and in some solids, but in most practical chemical contexts the proton is viewed as a hydrated, solvated species. The hidrogénion thus represents the fundamental proton donor in aqueous chemistry and biological processes.