Lewis Acids and Bases
The Bronsted definition of acids and bases refers specifically
to proton transfer. There is a more general way to think of acid-base
chemistry (that still includes Bronsted acid-base chemistry) called
Lewis acid-base theory. In this theory, a Lewis acid is an electron
pair acceptor. A Lewis base is an electron pair donor.
The reaction between CaO and CO2 is an example
of a Lewis acid-Lewis base reaction.
CaO is ionic so the net reaction occurs between the oxide
ion and carbon dioxide. The oxide ion donates an electron pair to the
carbon dioxide while the carbon dioxide accepts the electron pair.
The oxide ion is a Lewis base and CO2 is a
Lewis acid in this reaction. Although there are no protons to transfer,
this is still an acid-base reaction.
Reactions that undergo proton transfer can still be considered
from the standpoint of electron pair donation and acceptance as seen
below.
This reaction can either be thought of as electron pair
donation from the oxide or proton donation from the water with the same
result.
