Definition of hydronium ion in US English:

hydronium ion


  • The ion H₃O⁺, consisting of a protonated water molecule and present in all aqueous acids.

    • ‘Some examples of positively charged electrophiles are the hydronium ion, nitronium ions, metal ions, and carbocations.’
    • ‘Metals high on the activity series react more vigorously with oxidants including the halogens and the hydronium ion than those lower on the scale.’
    • ‘A hydronium ion, however, disrupts this structure because it can accommodate a maximum of three hydrogen bonds.’
    • ‘In response to that stress, the conjugate base reacts with the hydronium ion, producing more carbon dioxide which is removed from the system by increasing respiration.’
    • ‘Instead of floating free, hydrogen ions combine with water molecules to produce a positively charged hydronium ion.’


Early 20th century: hydronium, from German (a contraction).


hydronium ion

/hīˌdrōnēəm ˈīˌän/