Question

With the assumption that the ammonium ion is formed from the reaction between ammonia and hydrogen ion, describe the formation of bond between these two species and state the type of bond formed.

Answer 1

Ammonia is an inorganic molecule containing nitrogen as the central atom. Three hydrogen atoms are covalently bonded to the central nitrogen atom and the two remaining electrons are present as a lone pair in the hybridized orbitals of ammonia.

Complete answer:
The ammonium ion is a positively charged species that contains nitrogen atoms as the central atom connected to four hydrogen atoms. All four hydrogen atoms in an ammonium ion do not form the same type of bond with the central atom.
Assuming that the formation starts with the reaction between hydrogen ions and ammonia, the reaction can be called an acid-base reaction due to the ability of ammonia to act as a Lewis base and the ability of hydrogen ions to act as Lewis acid. The presence of lone pair on the nitrogen atom of ammonia makes it electron rich in nature and a positively charged hydrogen ion simply contains a proton and is therefore electron deficient in nature.
Due to the absence of vacant d-orbitals, nitrogen cannot extend its covalency to form five bonds or unpair the electrons present in its hybrid orbitals. As a result, the nitrogen atom temporarily donates or lends its pair of electrons to the electron deficient hydrogen ion.
The bond formation between nitrogen and hydrogen ions is such that even though it appears to be a conventional bond consisting of two atoms sharing two electrons, both the electrons are contributed by the nitrogen atoms. This is called a coordinate-covalent bond. The donation of its electron pair creates a positive charge on nitrogen and neutralizes the positive charge on the hydrogen atom.
${H^ + } \leftarrow :N{H_3} = N{H_4}^ +$
$\Rightarrow$ Thus, ammonium contains a coordinate covalent bond between the nitrogen atom and hydrogen ion.

Note:
Ammonia can be described as a Lewis base due to its electron rich nature or as a Bronsted base due to its tendency to accept hydrogen ions. In both cases the end product of the reaction between ammonia and hydrogen ion is the ammonium ion.