Beyond Water: How Chemists Redefined Acids and Bases

Science · Published 31 October 2026 Swipe more like this →

In short: For years, chemistry relied on a narrow view of acids and bases tied strictly to water. The Brønsted-Lowry theory shattered this limitation by focusing on the movement of protons rather than just ions, providing a more predictive framework for how chemicals interact in various environments.

The Brønsted-Lowry theory represents a significant expansion over the earlier Arrhenius theory. While the Arrhenius model was limited by its focus on aqueous solutions and specific ions like hydroxide, the Brønsted-Lowry framework defines acids as proton donors and bases as proton acceptors. This shift allows chemists to understand acid-base behavior in a much broader range of chemical contexts. Johannes Nicolaus Brønsted, a chemist from Denmark, along with Thomas Martin Lowry of England, created this concept. It serves as an essential tool for filling the gaps left by previous chemical models.

At the heart of this theory is the concept of equilibrium. When an acid and base react, they form conjugate acid-base pairs through a dynamic process where reactants can reform from products. For example, in a reaction between hydrochloric acid (HCl) and ammonia (NH3), the hydrogen ion transfers to the ammonia. This creates two distinct pairs: the HCl/chlorine ion pair and the ammonium ion/ammonia pair. The direction of this equilibrium is dictated by the relative strengths of the substances involved. The reaction is represented using double arrows to show that products can re-form reactants in a dynamic process. The equilibrium favors whichever side contains the weaker acid and base.

A key distinction of Brønsted-Lowry is that it does not require the presence of hydroxide ions, unlike the Arrhenius theory. However, even Brønsted-Lowry has a successor: the Lewis theory proposed by Gilbert Newton Lewis. While Brønsted-Lowry focuses on protons (hydrogen ions), Lewis chemistry looks at electron pairs. In the Lewis model, bases are electron-pair donors and acids are electron-pair acceptors, providing an even broader scope for chemical analysis. For instance, ammonia acts as a Lewis base because it has an electron pair on its nitrogen atom. This allows it to form bonds with substances like boron trifluoride.

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