amonio

Amonio, or ammonium, refers to the ammonium ion, NH4+. It forms by protonation of ammonia (NH3). In water NH4+ is in equilibrium with NH3 and H+, described by NH4+ ⇌ NH3 + H+. The pKa of NH4+ is about 9.25 at 25 °C, so at typical biological pH values the ammonium ion is the predominant form. Its geometry around nitrogen is tetrahedral, and it carries a +1 charge.

Salts of ammonium arise when NH4+ pairs with various anions, such as chloride, nitrate, sulfate, or phosphate. Common examples include ammonium chloride (NH4Cl), ammonium nitrate (NH4NO3), and ammonium sulfate ((NH4)2SO4). These compounds are typically white crystalline solids and are highly soluble in water.

In biological and environmental contexts, ammonium results from the microbial degradation of organic nitrogen and from excretion. Plants can take up NH4+ as a nitrogen source; bacteria may oxidize it to nitrite and nitrate in nitrification, connecting to the nitrogen cycle.

Industrial and practical uses include fertilizers, buffering and chemical synthesis, gas absorption, and the production of polymers. Safety considerations: ammonium salts are generally of low acute toxicity but can irritate skin, eyes, and respiratory tract in high concentrations; heating or reaction with strong bases can release ammonia gas.