an ion NH4+ or radical NH4 derived from ammonia by combination with a hydrogen ion or atom and known in compounds (as salts formed by reaction of dry or aqueous ammonia with acids) that resemble in pr, ammoniaagi (NH3) ja vesiniku iooniga reageerimisel (protoneerimisel) tekkinud väga ebapüsiv ioon, mis moodustab tavaliselt hapetega ammooniumi sooli