Lewis Concept of Acid and Base

According to Lewis Concept of Acid and Base- the species which can accept pair of electron or electron-pair acceptors are called acids. (Electron pair donor-acceptor system)

According to this concept, the species (charged or uncharged) which can accept pair of electron or electron-pair acceptors are called acids. The species which can donate a pair of electron or electron-pair donors are called bases.

Let us consider the following chemical reaction

H3N: + F3B H3N →BF3

In this reaction, NH3 acts as a base because it donates one pair of electrons, and BF3 acts as an acid because it accepts the pair of electrons. Lewis acids are also called electrophile or electrophilic reagents. Some examples are CL–, Br–, H2O, NH3, etc.

Advantages:-

1. It also includes those reactions in which no photons are involved.
2. It is a more common and extended concept than the Bronsted-Lowry concept
3. It explains the basic characters of metallic oxides and acidic characters of non-metallic oxides.

Limitations of the Lewis concept of acid and base:-

1. According to the concept, a co-ordinate covalent bond mostly formed when acid and base combine but there are many acid-base reactions in which a no-ordinate covalent bond is formed. For example:-

HCL + NaOH → Na+CL– + H2O

(acid)    (base)

1. It does not explain the strength of acid and base because it doesn’t consider the ionization process.

       An acid-base reaction is spontaneous and occurs rapidly but many lewis acid-base reactions are very slow.