Lewis Acid and Base in Reaction

[KMcFarland_2L]

When given a reaction, how do you identify which is the Lewis acid and which is the Lewis base in the reaction?

[Sydney Lam_2I]

Hi!

So a lewis acid will be a molecule or ion that accepts an electron (so look for molecules that are able to hold more electrons) while lewis base will be a molecule or ion that is more likely to give off electrons.

[Gabby Magat 3F]

An example for a Lewis acid would be a molecule with an electron deficient central atom (or a central atom with a positive formal charge).

Likewise, an example for a Lewis base would be a molecule with excess electrons, like lone pairs!

[AnnaNovoselov1G]

A Lewis acid can accept a pair of nonbonding electrons and a Lewis base can donate a pair of nonbonding electrons.

In the example, you can see that NH3 has a lone pair of electrons. The BF3 can react with it to form the stable compound NH3BF3
The NH3 acts as a Lewis acid and the BF3 acts as a Lewis base

[OwenSumter_2F]

Also make sure to take into account that Lewis acids and bases correspond to donating lone pair electrons, while Bronsted acids and bases correspond to donating H⁺ ions.