Ammonia, NH3

Ammonia is a colorless gas with an unpleasant smell. The NH3 molecule has a pyramidal form with triangular sides. Nitrogen is more electronegative than hydrogen which makes the molecule polar.

Two variants of presenting ammonia. Three hydrogen atoms are bound to a nitrogen atom in the NH3 molecule. A nonshared electron pair “lone pair” is shown to the right, giving the electron arrangement around nitrogen a nearly tetrahedral symmetry.


Ammonia is used as refrigerant in industries or store freezer cases. The gas is also a common chemical in chemical factories for producing fertilizers, nitric acid and other nitrogen containing compounds. Dry ammonia is flammable in contact with oxygen.

Ammonia is a common weak base for instance used in household cleaning solutions. The gas is easily dissolved in water, forming an alkaline solution according the equilibrium reaction:

NH3 + H2O ↔ NH4+ + OH-


Therefore ammonia is dangerous for the lungs and causes irritated eyes or skin.

Ammonia gas is known to show a strong absorption at 0.8 cm-1 or 12.5 mm wavelength in the microwave region. When the NH3 molecule is excited, once every 20.9 µs (microseconds) the nitrogen atom passes through the base forming a pyramid at the other side and 20.9 µs later it returns to its original position. This vibration back and forth has a frequency of 23 870 MHz and is denoted the ammonia resonator.


IR spectrum of ammonia, NH3

The characteristic peaks in the IR spectrum of ammonia come from the N-H bonds. At 3400 cm-1 (2.9 µm) the absorption is due to N-H strechings. The strong peaks at 1800 (5.6 µm) and 1000 cm-1 (10 µm) are caused by H-N-H scissoring and N-H wagging, respectively.