BronstedLowry

Bronsted-Lowry theory is a model of acid-base chemistry proposed independently by Johannes Nicolaus Bronsted and Thomas Martin Lowry in 1923. It defines acids as substances that donate protons (H+) and bases as substances that accept protons, emphasizing the transfer of a proton during a reaction.

In a Bronsted-Lowry reaction, an acid HA donates a proton to a base B, producing the conjugate base A− and the conjugate acid BH+. The concept of conjugate acid-base pairs is central: every acid has a corresponding conjugate base, and every base has a conjugate acid. For example, HCl donates a proton to water to form Cl− and H3O+, illustrating proton transfer in aqueous solution.

The theory extends beyond water and aqueous solutions. It applies to reactions in non-aqueous solvents and even in the gas phase, making it more general than the Arrhenius definition. Acid strength is related to the stability of the conjugate base: stronger acids have weaker conjugate bases, and weaker acids have stronger conjugate bases. The position of equilibrium in acid-base reactions is often described by pKa values in a given solvent.

Bronsted-Lowry chemistry is foundational in organic and biochemistry, where many functional groups participate in proton transfer, and substances such as water and amino groups can act as both acids and bases (amphoteric behavior). While highly influential, the Bronsted-Lowry model is complemented by the Lewis definition of acids and bases, which encompasses reactions that do not involve proton transfer.