the Arrhenius Model
The Arrhenius Model states that an acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in an aqueous solution while bases contain hydroxide and ionize to produce hydroxide ions in aqueous solutions.
THe Bronsted-Lowry model
The Bronsted-Lowry Model describes an acid as a hydrogen-ion donor while describing a base as a hydrogen-ion acceptor.
The Lewis model
The Lewis Model models acids as electron-pair acceptors and bases as electron-pair donors.