Question

Which of the following is not Lewis acid?

• A. $FeC{l}_3$
• B. $AlC{l}_3$
• C. $B{F}_3$
• D. $N{H}_3$

Answer 1

Answer: (D)

Electron deficient compounds or electron acceptors are Lewis acids.
(i) $B{F}_3$ and $AlC{l}_3$ are Lewis acids because B in $B{F}_3$ and Al in $AlC{l}_3$ are electron deficient atoms (They have 6 electrons each in their valence shell)
(ii) $FeC{l}_3$ is Lewis acid because it can accept electrons in vacant d orbital.
(iii) $N{H}_3$ is not Lewis acid because it has lone pair of electron (at N).
Infact it is Lewis base (there fore it is electron donor.)