In Arrhenius, we are limited to cases in which water is the solvent (this is assumed by Arrhenius). An acid will dissolve in water to produce H
ions, while a base will dissolve in water to produce O
Bronsted and Lowry state that an acid is any substance that will donate a proton (meaning an H
ion). This includes the case where the donation of the proton is made to a water molecule (which therefore includes everything Arrhenius would have considered), but allows for donation of protons to many other substances, opening the door for general acid-base reactions (proton-transfer reactions) such as
(Bronsted and Lowry also change our thinking of what makes a substance a base. All that is required is that a particle (atom, molecule or ion) be able to acquire a proton, and that particle is a base. Check out the role of N
The Lewis definition goes this one further in stating that an acid is a substance that can receive an electron pair (meaning the lone pair of a particle) and that a base is a substance that can donate a lone pair.
Again, this definition includes all cases that fit into the B-L scheme, because the H
proton Bronsted and Lowry refer to is a proton with an empty orbital. This orbital can bond with the lone pair of a particle such as the ammonia molecule (the N atom has a full orbital not used to bond to the three H atoms, hence a lone pair).
However, Lewis also includes cases in which the H
proton is not the particle being transferred, and so broadens the concept of acids and bases to include many more cases. For example
would not be an acid-base reaction according to Bronsted-Lowry, but does qualify in the Lewis sense.