ammoniumjonen

The ammonium ion, NH4+, is the positively charged species formed when ammonia (NH3) accepts a proton; in Norwegian and Danish, it is called ammoniumjonen. It is the conjugate acid of ammonia and is found in a wide range of salts, such as ammonium chloride (NH4Cl) and ammonium sulfate ((NH4)2SO4).

In terms of structure, the ion adopts a tetrahedral geometry around nitrogen, with four N–H bonds and no lone pair on nitrogen. The overall charge is +1, making it a common counter-cation in inorganic and organic salts.

In aqueous solution, NH4+ is a weak acid. It can donate a proton to water to form NH3 and H3O+. The acid dissociation constant is pKa ≈ 9.25 at 25°C. Thus, about all NH4+ remains protonated at neutral pH, while stronger bases can convert it back to NH3.

Ammonium salts are highly soluble in water and occur widely in nature and industry. They include fertilizers (ammonium sulfate, ammonium nitrate), feedstocks for chemical synthesis, and buffering agents in laboratory work. In soils and ecosystems, ammonium is produced by microbial metabolism and serves as a nitrogen source for plants; it is also a key intermediate in the nitrogen cycle.

Ammonium salts are generally of low to moderate toxicity but can irritate the skin, eyes, and respiratory tract. Heating or reaction with strong bases may release ammonia gas, which is irritating and toxic at high concentrations.