Johannes Nicolaus Brønsted

Danish chemist

• Born: February 22, 1879; Varde, Denmark
• Died: December 17, 1947; Copenhagen, Denmark

Twentieth-century physical chemist Johannes Nicolaus Brønsted was born in Denmark and studied at the University of Copenhagen. He is known for revising the definition of acids and bases, focusing on the chemical reactions themselves.

Primary field: Chemistry

Specialties: Physical chemistry; inorganic chemistry; thermodynamics

Early Life

Born in the town of Varde, Denmark, on February 22, 1879, Johannes Nicolaus Brønsted was introduced to science and mathematics at an early age by his father, a civil engineer who specialized in irrigation. Brønsted’s mother died shortly after his birth. His father soon remarried, and the financially-stable family spent the next years living on a farm outside of Varde. When Brønsted was fourteen, his father died. It would have been customary at the time for Brønsted to find work and to support the family, but his father’s wife was determined that he should be able to pursue his intellectual and artistic interests. She moved the family to Copenhagen, the center of Danish culture and academia, and enrolled Brønsted in one of the best schools there.

With his family’s encouragement, Brønsted passed his university entrance examination and matriculated into Copenhagen’s Polytechnic Institute in 1897, where he completed a practical degree in engineering two years later. At the Institute he met Charlotte Louise Warberg, a fellow student who would become one of the first female engineers in Denmark. The two married in 1903.

Rather than beginning work immediately, Brønsted decided to further his studies at the University of Copenhagen. While there, he completed a degree in chemistry in 1902, followed by a doctorate in chemistry in 1908. His sister, Ellen, found similar success pursuing sculpture and painting at the Academy of Fine Arts in Copenhagen. Through her influence, Brønsted also took up painting, a passion that would remain for the rest of his life. Soon after his graduation in 1908, he found placement as a professor of physical and inorganic chemistry at the chemical laboratories of the University of Copenhagen, where he had been appointed as assistant in 1905. The professorship allowed him to begin his eventually groundbreaking research in thermodynamics.

Life’s Work

Brønsted began his research in electron affinity, the amount of energy that is released in the creation of a negative ion from the combination of an electron and a neutral atom. He published his first papers on the subject while he was still a student. This research led him to his major discovery, the protonic theory of acid-base reactions. The reactions that occur between acids and bases had been the subject of major chemical study for centuries, but there had also been constant debate and revision among chemists regarding the way those reactions were defined. Brønsted offered a new way of understanding acid-base reactions, arguing that their core component could be narrowed down to the fact that acids give a hydrogen atom to bases. The same year that Brønsted put forth this theory, 1923, an English chemist named Martin Lowry made the same announcement. As both scientists came to their conclusions independently of one another, the protonic theory is commonly called the Brønsted-Lowry acid-base theory.

The method of looking at acids and bases that Brønsted pioneered allowed chemists to view acid-base reactions in a new light. To start, the fundamental definition of acids and bases was revised. In Brønsted’s theory, an acid is any compound that has a proton (a hydrogen ion) it can donate, while a base is any compound that has the ability to take on an additional hydrogen ion. The reaction, such as in the common example of vinegar being added to baking soda, occurs because of the energy being used in the hydrogen ion’s process of transference. Brønsted also introduced two new terms: the conjugate base, which is what remains after the hydrogen ion leaves the acid; and the conjugate acid, which is the particle created when the hydrogen ion is added to the base. Thus, any pair of molecules that can react by transferring a hydrogen ion are commonly called a “conjugate acid-base pair.” These new definitions broadened the way chemists could consider acid-base reactions.

Previously, scientists had viewed acid-base reactions in terms of salts and solvents, a perspective that considered the reaction to be an aspect of the acids and bases partially neutralizing one another. In this theory, acids produced hydrogen ions and bases produced hydroxide ions, the two of which would combine to create water. Introduced by the Swedish chemist Svante Arrhenius in the 1880s, the theory did not account for many of the acid-base reactions that could be explained in the Brønsted-Lowry theory.

Brønsted’s new theory established him as an important figure in chemistry. He traveled to the United States, partially to visit other chemists and partially to serve as a visiting professor at Yale University in New Haven, Connecticut, from 1926 to 1927. Many of the scientists he visited during this time returned the favor, visiting him in Copenhagen, and with those contacts he raised enough money to open the Physicochemical Institute at Blegdamsvej, a research laboratory often called the Brønsted Institute. He moved his family to the new laboratory in 1930. While there, Brønsted took on pupils and furthered his study of acid-base reactions, narrowing his research interests down to the field of catalysis.

Catalysis refers to the effects on a chemical reaction by a catalyst, which is any material that changes the reaction without being consumed in the process. Catalysts typically contribute to reactions by lowering the amount of energy needed to create a reaction. This results in more collisions between molecules and, subsequently, greater or different reactions than would occur without the catalyst present. Brønsted created an equation that measures the relationship between the strength of an acid and the resulting catalytic activity. The Brønsted catalysis equation, as it is commonly called, took the basic ideas of his early work and applied them to a specific circumstance, allowing for much more accurate and specific predictions when working with acid-base catalytic reactions.

When World War II broke out in Europe, Brønsted’s life took an unexpected turn. While he continued to work on his chemical studies, he also actively and publicly opposed the Nazis. Although doing so put his life in danger, it also moved him further into the public eye. When the war was over, many people encouraged Brønsted to run for political office. Since he was usually a reserved and introverted man, his friends and family were surprised when he accepted the encouragement and ran for office. In 1947, Brønsted was elected to the Danish parliament. He fell ill that year, however, and died on December 17, 1947, before ever taking his seat. He was sixty-eight years old.

Impact

The Brønsted-Lowry theory of acid-base reactions remains one of the most widely used and accurate theories of acids and bases to this day. The study of acid-base reactions is somewhat unique in that, depending on the specifics of the reaction, different theories and sets of definitions are more useful than others. It is for this reason that, in the years following the Brønsted-Lowry theory, additional theories have also gained prominence. Some of these theories are more specific, emphasizing the role of oxygen or the strength of charges, while others attempt to be more general. While these theories and definitions are useful at times, the ideas Brønsted put forth remain the most common. When chemists refer to acids and bases without specifying otherwise, they are generally referring to the Brønsted-Lowry definition.

The general scope of Brønsted’s theory, in contrast to more exclusionary definitions of acids and bases, allowed for a number of related concepts to be discovered. Water, for instance, is able to act as both an acid and a base, depending on whether it gives or takes a hydrogen ion in a particular circumstance. This is true of several compounds, which are called amphoteric compounds. As with most fundamental theories, the greatest impact of Brønsted’s work on acids, bases, and catalysts was not so much the definition itself, but the way that definition could be applied. His focus on reactions gave chemists a new way of understanding the chemical process, as well as a new way of conceptualizing and experimenting while in the laboratory.

Bibliography

Houston, Paul L. Chemical Kinetics and Reaction Dynamics. Mineola: Dover, 2006. Print. Covers the principles, theories, and rates of chemical kinetics and reactions at the gas, liquid, solid, and molecular levels. Includes acid-base catalysis.

Klein, David R. Organic Chemistry. Hoboken: Wiley, 2011. Print. A textbook study of organic chemistry containing a section on acids and bases and the Brønsted-Lowry theory. Illustrations, glossary, index.

Smith, Michael B. Organic Chemistry: An Acid-Base Approach. Boca Raton: CRC, 2011. Print. Defines modern organic chemistry on the basis of acid-base reactions, with particular emphasis on reactions as defined by Brønsted-Lowry. Illustrations, bibliography, index.

Solomons, T. W. Graham, and Craig B. Fryhle. Organic Chemistry. 10th ed. Hoboken: Wiley, 2011. Print. Covers the modern concepts of organic chemistry, beginning with an introduction to acids and bases. Illustrations, glossary, index.