The ammonium ion,
An electrophile is a species that accepts a pair of electrons to form a new covalent bond.
This should sound familiar. It is the definition of a Lewis acid!
In the reaction
At the moment of collision between the two ions, a lone pair of electrons on the hydroxide ion forms a bond to the
Simultaneously, the electron pair on the other side of the
The electrophilic atom in the
The ammonium is accepting electrons, so we usually call it a Lewis acid rather than an electrophile