ammooniumiooni

Ammooniumiooni is the ammonium ion, a positively charged polyatomic ion with the formula NH4+. The name ammooniumiooni appears in some Finnish-language sources as a direct transliteration of ammonium ion; in English, the standard term is ammonium ion. The ion forms when ammonia (NH3) is protonated: NH3 + H+ → NH4+. In aqueous solution, NH4+ coexists with NH3, and their relative amounts depend on pH. The pKa for the conversion NH4+ ⇌ NH3 + H+ is about 9.25, making ammonium a weak acid.

Structure and properties

Ammonium ion has a tetrahedral structure with four N–H bonds and a central nitrogen bearing a +1 formal charge. All hydrogen atoms are equivalent, and there are no lone pairs on nitrogen in NH4+. The ion is highly soluble in water and forms a wide range of salts, known as ammonium salts (for example, ammonium chloride, ammonium sulfate, and ammonium nitrate). In solid form, ammonium salts are typically colorless and hygroscopic, depending on the counterion.

Occurrence and uses

Ammonium salts are common in agriculture as nitrogen fertilizers, supplying plant-available nitrogen. They are also used in chemical synthesis, buffer systems, and cleaning products. In the nitrogen cycle, ammonium can be oxidized by bacteria to nitrite and then nitrate in a process called nitrification. Ammonium compounds can release ammonia under certain conditions, which contributes to odor and environmental impacts.

Safety and handling

Ammonium salts are generally of low to moderate toxicity but can cause irritation in higher concentrations. In the environment, excessive ammonium can contribute to eutrophication and water quality issues. Proper storage and handling follow standard chemical-safety guidelines.

See also

Ammonia, ammonium salts, nitrification, urea cycle.