In 1923, scientists Johannes Bronsted and Thomas Lowry developed a system for better understanding how acids and bases interacted. This was intended as an alternative to the Arrhenius theory and the later-developed Modified Arrhenius theory.
In order to understand Bronsted-Lowry’s concept, one must consider what a hydrogen atom is, as well as what a hydrogen ion is, and how they interact in solutions. Remember that they both have one proton and zero neutrons, and the ion does not have an electron. Considering this, we can say that a Hydrogen ion is in essence a proton. The Bronsted-Lowry theory states that an acid is a “proton donator”, and a base a “proton acceptor”. Some molecules have the capacity to act as both of these, and they are said to be called amphoteric or amphiprotic, such as water or carbonic acid. These can be easily identified by the fact that they have a hydrogen atom as a component element, as well as a negative charge (except for water, which is a special case that ionizes into either hydronium or hydroxide).
In a Bronsted-Lowry reaction, the stronger acid will act as such, and likewise with the strongest base. For example, if the amphoteric carbonic acid was added to a strong acid such as hydrochloric acid, then the hydrogen ion would be donated from the HCl to the HCO3-. This results in a set of net products of water, chloride ions, and carbon dioxide gas.
Note that the Bronsted-Lowry concept permits the discussion of conjugate acids and bases. These are the same compound in essence, except the acids will have one more hydrogen ion than the bases.
A Bronsted-Lowry reaction will be more likely to process if the acid is stronger. This phenomenon is because the stronger the acid, the weaker the force that it uses to hold its proton to itself, thus leading to the higher degree of reaction when a strong acid is mixed with a base.
The Bronsted-Lowry theory allows for a new level of understanding about the interactions of everyday chemicals. It places a premium value on how the hydrogen ion (and therefore the hydronium ion) can come off an acid to create a conjugate base, and how these chemicals interact. It is imperative for the success of modern science that new theories be developed and considered when they have implications like those of Bronsted-Lowry.