Explanation:
Lewis definition of Acids and Bases
Chemical species which are capable of accepting electron pairs or donating protons are called Lewis acid.
Chemical species which are capable of donating electron pairs or accepting protons are called Lewis base.
Bronsted definition of acids and bases
Chemical species which are capable of donating H+ are called Bronsted acids.
Chemical species which are capable of accepting H+ are called Bronsted bases.
So all Bronsted acids are Lewis acids but all Lewis acids are not Bronsted acids.
For a chemical species to behave as Lewis acid, they must have:
- Incomplete octet
- Double bond
- Vacant d-orbitals
For example, in BF3, octet of boron is incomplete, so it can accept a pair of electron and behaves as Lewis acid.
For a chemical species to behave as Lewis base, they must have:
For example, NH3 and OH, both N and O have lone pairs of electrons, hence behave as Lewis base.
