Ammonia

Ammonia is probably the industrial molecule that most changed human history in the 20th century. Before its large-scale synthesis, agricultural nitrogen came from Peruvian guano, Chilean saltpetre or biological fixation cycles — geographically concentrated sources insufficient for a growing population. The Haber-Bosch process, developed between 1909 and 1913, made it possible to convert inert atmospheric nitrogen (N₂) into usable NH₃, unlocking mass fertiliser production. It is now estimated that roughly half of the nitrogen in the human body, via the food chain, originates from synthetic ammonia.

Chemically, NH₃ owes its properties to the lone pair on the nitrogen atom, which makes it a Brønsted base (proton capture to form NH₄⁺) and a nucleophile in many organic reactions (amide, amine and urea synthesis). The pyramidal geometry around nitrogen — HNH angle of about 107° — comes from the repulsion between this lone pair and the three N–H bonds. The high water solubility (482 g/L at 24 °C) arises from hydrogen bonds with H₂O molecules, and the resulting aqueous solution ("ammonia water") is a routine Lewis base in the lab.

Industrially, NH₃ is also a refrigerant (R-717) widely used in large-scale food-grade refrigeration thanks to its excellent thermal capacity and zero global-warming potential (GWP = 0). Its main drawback is toxicity: odour detectable at a few ppm, eye and respiratory irritation above that, lethality at high concentrations in confined spaces. The Haber-Bosch process alone consumes about 1–2 % of global primary energy — making it a major target for current decarbonisation efforts (green ammonia produced from electrolytic hydrogen).