ammoniumion

The ammonium ion is a polyatomic cation with the chemical formula NH4+. It is formed when ammonia (NH3) accepts a proton (H+). This protonation reaction can occur in aqueous solutions or in the gas phase. The nitrogen atom in the ammonium ion is covalently bonded to four hydrogen atoms, with one hydrogen atom carrying a formal positive charge. This positive charge is delocalized across the entire ion.

Ammonium ions are commonly found in salts, such as ammonium chloride (NH4Cl) and ammonium sulfate ((NH4)2SO4). These salts are often soluble in water, dissociating into ammonium cations and their respective anions. In biological systems, ammonium ions play a crucial role in nitrogen metabolism. They are a product of protein and nucleic acid breakdown and are converted to urea in the liver of mammals or to uric acid in birds and reptiles for excretion.

The ammonium ion is a weak acid, capable of donating a proton to form ammonia. Its conjugate base is ammonia. This acid-base behavior is important in various chemical and biological processes, including buffering systems. Ammonium ions are also used in fertilizers due to nitrogen's essential role in plant growth. The presence of ammonium in the environment can be an indicator of pollution, particularly from agricultural runoff and wastewater.