Why is NH3 (Ammonia) basic?
Ammonia acts as a base when mixed in water. According to Lewis theory, ammonia is described as base as it has one lone pair of electrons on the nitrogen atom. A Lewis base donates electrons while Lewis acid accepts electrons. According to valence shell electron pair repulsion (VSEPR) theory the shape of the ammonia molecule was determined as Trigonal pyramidal. This shape has a bond angle of 107.8 degrees. There are 5 valence electrons contributed by nitrogen and 3 electrons by every hydrogen atom in ammonia. All together 8 electrons or 4 pairs of electrons are distributed around the molecule in tetrahedral shape. The shape of the molecule is tetrahedral due to the arrangement of electrons in this shape.
The bonding between nitrogen and three hydrogen atoms occurs with three lone pairs of electrons. One lone pair of electrons remains free on the nitrogen atom itself. As the lone pair repels the other electrons, the usual tetrahedral arrangement is changed. The actual tetrahedral angle should be 109.5 degrees, while the tetrahedral angle of ammonia is measured as 107.8 degrees.
This lone pair of electrons on the nitrogen atom of ammonia plays important role in giving the molecule basic characteristics. So, ammonia is considered as a base as it is proton acceptor as well as electron donor. Ammonia is classified as a weak base. A 1M ammonia solution will have the negative logarithm of hydrogen ion concentration as 11.6. The amount of this solution that is neutralized by a strong acid will be around 99.4 percent. Ammonia is also found to form salts by reacting with acids. This shows that ammonia is basic. Liquid ammonia or ammonium hydroxide is also proved to be acting as basic solvent. Ammonium hydroxide is a base which is widely used to dissolve alkali metals in order to prepare an electrically conducting solution. This type of basic solutions possesses solvated electrons to conduct electricity.