-American chemist G. N. Lewis formulated a definition. He defined what we now call a Lewis base as a substance that can donate a pair of electrons.

 

-A Lewis acid is a substance that can accept a pair of electrons. For example, in the protonation of ammonia, NH3 acts as a Lewis base because it donates a pair of electrons to the proton H+, which acts as a Lewis acid by accepting the pair of electrons. A Lewis acid-base reaction, therefore, is one that involves the donation of a pair of electrons from one species to another. Such a  reaction does not produce a salt and water.

 

-The significance of the Lewis concept is that it is more general than other definitions. Lewis acid-base reactions  include many reactions that do not involve Bronsted acids. Consider, For example, the reaction between boron trifluoride (BF3) and ammonia to form an adduct compound.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

-The B atom in BF3 in sp2-hybridized. The vacant, unhybridized 2pz orbital accepts the pair of electrons from NH3. So BF3 functions as an acid according to the Lewis definition, even though it does not contain an ionizable proton. Note that a coordinate covalent bond is formed between B and N atoms, as is the case in all Lewis acid-base reactions.

 

-Another Lewis acid containing Boron is boric acid. Boric acid (a weak acid used in eyewash)is an oxoacid with the following structure.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Source:

Book- Chemistry Raymond Chang- Author

 

 

 

Written by: Glenn Edgardo Malaca

Revised.