How can I identify a Lewis base?
You draw the Lewis structure and look for a pair of electrons that can form a bond to another atom.
A Lewis base is a molecule or ion that can donate a pair of electrons to form a bond.
An atom, ion, or molecule with a lone-pair of electrons can be a Lewis base.
Each of the following can "give up" their electrons to something that will accept them:
HO:⁻, :N≡C:⁻, CH₃COO:⁻, :NH₃, H₂O:, and :C≡O:
In the above example, the ammonia is the Lewis base because it donates its lone pair of electrons to H⁺ to form a bond.
In organic chemistry, many compounds with π electrons act as Lewis bases.
The alkene above is a Lewis base, because it donates its π electrons to form a bond to the H⁺.
Here’s a video on identifying Lewis bases and acids.