The formation of the ammonium ion is an example of coordinate 

The formation of the ammonium ion is an example of coordinate .

To get a better understanding of how the ammonium ion, ##"NH"_4^(+)##, is formed, start with the of ammonia.

The molecule has a total of 8 , 5 from nitrogen and 1 from each of the three hydrogen atoms.

The nitogen atom will bond with the hydrogen atoms via single bonds. Notice that you have a lone pair of electrons present on the nitrogen atom.

Now, a hydrogen ion, ##H^(+)##, which essentially is a proton, will be attracted to that lone pairs of electrons. The bond that is formed when a hydrogen ion is attached to the ammonia molecule is called a coordinate bond (or a dative covalent bond).

What you're essentially dealing with here is the reaction between a , which an electron donor, and a , which acts as an electron acceptor.

Using other terminology, ammonia acts as a nucleophile, which is a reactant that provides a lone pair of electrons for the formation of a covalent bond.

The nitrogen atom donates its lone pair of electrons to form a coordinate bond with the proton. These two electrons are now bonding electrons between nitrogen and the fourth hydrogen atom in ##"NH"_4^(+)##.

The bond is called coordinate (or dative covalent) because both bonding electrons come from one of the atoms that form the bond. In this case, nitrogen contributes both bonding electrons, since the hydrogen ion has no electrons to begin with.