Brønsted, Johannes Nicolaus (1879–1947)

Danish physical chemist whose work in solution chemistry, particularly electrolytes, resulted in a new theory of acids and bases, the theory of proton donors and proton acceptors, published in 1923.

Brønsted was born in Varde, Jutland, and studied at Copenhagen, where he became professor of physical and inorganic chemistry in 1908. In his later years he turned to politics, being elected to the Danish parliament in 1947.

Brønsted laid the foundations of the theory of the infrared spectra of polyatomic molecules by introducing the so-called valency force field in 1914. He also applied the newly developed quantum theory of specific heat capacities to gases, and published papers about the factors that determine the pH and fertility of soils.

Brønsted's new theory of acidity, published in 1923, had certain important advantages over that proposed by Swedish chemist Svante Arrhenius in 1887. Brønsted defined an acid as a proton donor and a base as a proton acceptor. The definition applies to all solvents, not just water. It also explains the different behaviour of pure acids and acids in solution. In Brønsted's scheme, every acid is related to a conjugate base, and every base to a conjugate acid.