BrønstedLowryKonzept

The Brønsted-Lowry concept, also known in German literature as the Brønsted-Lowry-Konzept, is a widely used model of acid-base chemistry. It defines acids as substances that donate protons (H+) and bases as substances that accept protons. The theory was developed independently by Johannes Nicolaus Brønsted and Thomas Martin Lowry in 1923 and refined the understanding of acid–base reactions beyond the limitations of earlier Arrhenius definitions.

In a Brønsted-Lowry reaction, an acid HA transfers a proton to a base B, yielding a conjugate base A− and a conjugate acid BH+. The reacting species form conjugate acid-base pairs: HA/A− and BH+/B. The position of equilibrium depends on the relative strengths of the acids and bases in the given solvent; a stronger acid has a weaker conjugate base, and vice versa.

Examples include HCl donating a proton to water to form H3O+ and Cl−, and NH3 accepting a proton from water to form NH4+ and OH−. The concept extends to non-aqueous solvents and even to gas-phase reactions, wherever proton transfer can occur.

The Brønsted-Lowry concept is more general than the Arrhenius model and sits alongside broader frameworks such as the Lewis definition, in which acids are electron-pair acceptors and bases electron-pair donors. In practice, Brønsted-Lowry acidity and basicity are assessed using conjugate-acid/base strength, pKa values, and the behavior of buffers.