Protolytic theory of acids and Bronsted-Lowry bases

The protolytic theory of acids and bases is on the verge of two sciences at once: physics and chemistry. With its help, the properties and nature of all bases and acids are described. Scientists are divided into two classes of substances that interact with each other.

The problem of theory

The protolytic theory of acids and bases helps to solve an important problem: to predict what products are formed as a result of their interaction and how this reaction will proceed. To do this, experts apply quantitative and qualitative features of acid and base.

There are several theories that differently interpret what are acids and bases. In different ways, they evaluate their other characteristics. In the final analysis, it depends on what the result of the reaction will be.

Conceptual chemical systems

The protolytic theory of acids and bases is extremely popular when one needs to find out how they interact in nature. It is widely used in industrial practice and the scientific field. Theoretical knowledge of the consequences of the interaction of bases and acids determine the formation of conceptual systems of chemistry, affect all sorts of theoretical concepts in virtually all chemical disciplines.

Evolution of knowledge about the interactions of acids and bases

The protolytic theory of acids and bases is one of the fundamental in chemistry. Key concepts were first formulated by scientists in the 17th century. At the same time, their content after that changed many times and was revised.

An English chemist of the seventeenth century Robert Boyle believed that the acids are the bodies whose atoms have sharp protrusions, and the bases are their pores. Therefore, in his opinion, the whole neutralization reaction is reduced to the fact that acid protrusions penetrated into the pores of the bases.

The theory of acids and bases was first proposed by the French pharmacist Nicola Lemeri. In 1675 he published the "Chemistry Course", in which he detailed the chemical and physical properties of substances based on their shape and structure. Lemery imagined that acids have sharp spines, because of which discomfort on the skin appears. He christened the bases with alkalis, assuming that their structure is porous. As a result, neutral salts are formed.

Already in the XVIII century, another French naturalist Antaun Lavoisier related the properties of acids to the presence of oxygen atoms in their composition. Its failure was demonstrated by the English chemist Humphry Davy and his French counterpart, Joseph Louis Gay-Lussac, who identified a number of acids that did not contain oxygen at all. Among them were halogenated hydrogen or hydrogen cyanide. In this case, a large number of oxygen-containing compounds were found which did not possess the properties of acids.

Contemporary representations

The concept of the protolytic theory of acids and bases changed significantly in the 19th century. Chemists began to consider as acids only those substances that are able to interact with metals and release hydrogen. Such conclusions were reached by the German scientist Justus von Liebig in 1839. It is he who is considered one of the founders of agrochemistry and organic chemistry.

In parallel with him, the Swedish mineralogist Jens Jacob Berzelius formulated the idea that it is necessary to refer to negative oxides of nonmetals to acids, while oxides with a positive charge are bases. This helped explain the basic properties of acids and bases. That is why the acidity and basicity of Swedes considered as a functional property of compounds. It was he who for the first time in the world attempted to predict the ultimate strength of the substances we are considering.

The main provisions of the protolytic theory of acids and bases were formulated after the work of another Swedish chemist, Svante August Arrhenius. In 1887, he summarized the theory of dissociation of electricity. After it there was a real opportunity to describe the properties of acids and bases based on the products of ionization of electrolytes. And thanks to the contribution of the Russian-German chemist Wilhelm Friedrich Ostwald, the theory was formulated for weak electrolytes.

In the twentieth century, American scientists Cady, Franklin and Kraus justified the theory of solvosystems. It began to be applied both to the provisions of Arrunius and Ostwald, and to all other solvents that could self-associate.

Nowadays, the protolytic theory of acids is most fully formulated by the Dane Johannes Nicolaus Brønsted and the American Gilbert Newton Lewis, who also dealt with nuclear physics and thermodynamics.

The Liebig theory

According to the Liebig hydrogen theory, the acid is a substance capable of reacting with metals, as a result of which hydrogen is formed. In this case, the concept of "foundation" Liebig did not enter at all.

Hydrogen and salt are formed as a result of the reaction. When reacting with strong acids, the reaction is manifested by metals. Today, the theory is used only to predict the interaction of substances containing hydrogen with metals in solvents.

The Arrhenius-Ostwald theory

Understanding what the protolytic theory of acids and bases of Arrhenius-Ostwald is, we note that all substances that form hydrogen cations in an aqueous solution are considered as acids in it. In this case, only substances with which a metal or ammonium cation is obtained in aqueous solution are considered as the bases.

As a result of the reaction, water and salt are formed. A dependence is observed when strong acids interact with strong bases. On the basis of this theory, it was possible to substantiate the division of electrolytes, and also the determination of the hydrogen index, which was extended to alkaline media, was introduced. It is also used in the hydrolysis of salts and bases containing salts. However, less often. The point is that this requires cumbersome calculations. While the proton theory is much simpler.

The Bronsted-Lowry theory

The protolithic theory of acids and bases of Bronsted - Lowry first appeared in 1923. Bronsted and Lowry formulated it independently of each other. Scientists have combined the concepts of acids and bases into a single whole.

According to their ideas, acids are molecules or ions that perform the role of proton donors in the reaction. At the same time, the bases are only those molecules or ions that are capable of attaching protons. In this theory, acids and bases have been determined protolytes. What is the essence?

The protolytic theory of acids and bases in chemistry reduces to the transfer of a proton from the acid to the base. And at this time, the acid, having lost the proton, itself turns into a base. And she can already add a new proton to herself. The base at this time becomes acid, forming a protonated particle.

Therefore, in any interaction of the substances we are considering, two pairs of bases and acids are involved. Bronsted calls them conjugated. These are the main provisions that allow us to formulate a protolytic theory of acids and bases. Protolytic reactions in this case proceed in two ways, because any substance, depending on the conditions, can be both acid and base.

Later, Bronsted developed the theory of acid-base catalysis, and Lowry worked on the optical activity of organic compounds.

Theory of solvosystems

The theory of solvosystems appeared during the development of ideas put forward by Arrhenius and Ostwald. Most often it is used in reactions with proton solvents. Three Americans offered it - Cady, Franklin and Kraus.

According to this hypothesis, the basis is the ionic solvent. It has the ability to disintegrate into individual ions in the absence of a solvent. In this case, the cation and anion. The first is the lithium ion, and the second is the lithium ion. The proton solvent used in the reaction is capable of transferring a proton from any neutral liquid molecule to another. As a result, an equal amount of anions and cations is formed.

The product of this reaction is solvent and salt.

This theory is used to predict the reactions between acids and bases in any solvents. It is also possible to control these processes with a solvent. The theory describes in detail the properties of substances that do not contain oxygen and hydrogen.

The Lewis theory

The theory of Lewis was formulated in 1923. It was based on the electronic representations available at that time in science. With their help, it was possible to maximally expand the definition of base and acid.

In chemistry there is the concept of "Lewis acid". It is an ion or molecule that has free electron orbitals, on which electronic pairs can receive. A vivid example are protons - hydrogen ions, as well as ions of certain metals, some salts and substances.

If there is no hydrogen in the Lewis acid, it is called aprotic.

Theory of Usanovich

The most general theory of acids and bases in 1939 was formulated by the Soviet chemist Mikhail Usanovich.

It is based on the notion that any interaction between the acid and the base will lead to a salt reaction. Thus, the acid is defined as a particle that cleaves cations from itself, including protons, and also adds anions and, in the first place, electrons to them.

At the same time, the base is a particle that has the ability to attach a proton or any other cation to itself. But it can also give away an electron or anion. The fundamental difference from the theory of Lewis is that the basis of the definitions of "base" and "acid" is not the structure of their electronic shell, but the sign of the charge of their particles.

However, in the theory of Usanovich there are shortcomings. The main of them - a large number of generalizations and fuzzy wording of the basic concepts. In addition, this theory does not allow quantitative predictions of the consequences of the interaction of acids and bases.