Lewis base is a electron pair donor, the species of molecules or ions which have a tendency to donate its free electron pair is then classified in the Lewis base. Examples of Lewis base is a halide ion (Cl-, F-, Br-and I-), ammonia, hydroxide ions, water molecules, compounds containing N, O, or S, a compound class of ether, ketone, a molecule of CO2 and other .
The figure above shows Lewis base with its free electron pair.
Lewis acids are electron pair acceptor. Examples of Lewis acids are H +, B2H6, BF3, AlF3, transition metal ions that can form complex ions such as Fe2 +, Cu2 +, Zn2 +, etc.
You might think that to be a Lewis acid will always be empty orbitals needed to accommodate the electron pairs donated by the Lewis base but this is not absolute because to be a Lewis acid is not always a species provides an empty orbital.
Reaction of Lewis acids and Lewis bases can be exemplified as follows:
So, that became the base electron donor and electron acceptor which becomes acid