Ammonia

Article

May 25, 2022

Ammonia, called nitrogen trihydride in the IUPAC systematic nomenclature or azano in the alternative nomenclature, is a nitrogen compound with the chemical formula NH3. It appears as a colorless, toxic gas with a characteristic pungent odor. It is very soluble in water to which it gives a clear basicity.

History

Ammonia, in the form of ammonium salt, was already known in the classical age: in Pliny's work there are references to a substance indicated as Hammoniacus sal, although it is not clear whether it referred to the substance that we now call salt of 'ammonium. The latter owes its name to the temple of Jupiter Ammon in the Siwa oasis in Egypt, where it was first identified as a substance in itself when it was accidentally observed in the ashes of dromedary dung burned by local camel drivers to keep warm. Ammonium salt was known to alchemists at least since the thirteenth century, when it appears in the writings of Albert the Great: in the fifteenth century the hermeticist Basil Valentine (Basil Valentine) discovered that ammonia could be obtained from ammonium salt by making it react with alkali . A short time later it was discovered that ammonium salt could also be obtained by distilling the horns and hooves of oxen and neutralizing the resulting vapors with hydrochloric acid: hence the ancient Anglo-Saxon name for ammonia, spirit of hartshorn. Pure gaseous ammonia was finally isolated in 1774 by Joseph Priestley who called it "alkaline air" and three years later (1777) Carl Scheele proved that it contained nitrogen: the stoichiometric composition of ammonia was discovered by Claude Berthollet in 1785. In the laboratories of the German chemical industry BASF, the industrial production of ammonia by Fritz Haber and Carl Bosch began in 1913.

Features

The shape of the anhydrous ammonia molecule is deformed tetrahedral; the nitrogen atom appears there with sp3 hybridization, occupies the central position and binds the three hydrogen atoms. The base is an equilateral triangle occupied by the three hydrogen atoms while the fourth vertex of the tetrahedron is occupied by a lone pair which is mainly responsible for all the properties of the molecule: formation of hydrogen bonds, basicity according to Lewis and according to Brønsted-Lowry, high electrical permittivity and dipolar moment, high solubility in water. The angle H-N-H is 107.5 ° and the symmetry elements are 1 rotation axis C3 and 3 reflection planes σv, while there is no inversion center i. According to the VSEPR terminology its representation is AX3E (trigonal pyramid). If suitably excited, the ammonia molecule can undergo Walden inversion, ie the non-bonding doublet can oscillate above and below the plane of the three hydrogen atoms; this inversion also extends to amines. the configuration inversion of ammonia in the low pressure gas phase was exploited to produce the first stimulated emission maser in 1953. At room temperature ammonia is a colorless gas with a very strong and suffocating pungent odor, it is irritating and toxic. In the presence of O2, therefore in the air, it can attack aluminum, copper, nickel and their alloys. It is a weakly basic compound and reacts with acids to form the respective ammonium salts. It has a reducing behavior, can also react explosively with oxygen, and combines with halogens to give halogenamines. It is among the best known and most studied non-aqueous polar solvents; its most characteristic property is to dissolve alkali metals forming intensely blue colored solutions with high electrical conductivity. Compared to water, ammonia has lower conductivity, lower electrical permittivity, lower density and viscosity, much lower freezing and boiling points. The ionic self-dissociation constant of ammonia liq