WHAT IS THE THIRD CHEMICAL REVOLUTION? - CULTURE VOCABULARY - 2024

The third revolution of chemistry refers to the advances that were made in the area of ​​this branch of science in the twentieth century, specifically between 1904 and 1924. Some of these were the delimitation of the concept of valence, the contributions of Lewis in regarding atomic configurations, covalent bonds, acids and bases, electronegativity and hydrogen bonds.

The most representative document of this time was the monograph by Gilbert Newton Lewis, On the valence and structure of atoms and molecules (Valence and the Structure of Atoms and Molecules), published in 1923.

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Characteristics of the third revolution of chemistry

On the valence and structure of atoms and molecules, the work of Gilbert N. Lewis, is the source of many of the current ideas of electronic theory on bonds and reactivity.

It was the key work of the third chemical revolution. Some of the most relevant contributions of this document are:

1- The bond formed through a pair of shared electrons

"… the chemical bond is, at all times and in all molecules, a pair of electrons that are held together…" (Lewis, 1923; cited by Jensen, 1995. Own translation).

2- The continuity of the bond and polarization

“… Due to the great difference between polar and non-polar substances, it can be shown how a molecule can go from a polar end to a non-polar one, according to environmental conditions. However, this does not occur per saltum, but occurs through imperceptible gradations… ”(Lewis, 1923; cited by Jensen, 1995. Own translation).

3- The relationship between the polarity of the bond and electronegativity

“… The pair of electrons that make up the bond can be found between two atomic centers in a position such that there is no electrical polarization, or it can be closer to one of the atomic centers, giving that atom a negative charge and, consequently, positive charge to the other atom… ”(Lewis, 1923; cited by Jensen, 1995. Own translation).

From this, it follows that the central atom is generally the most electropositive, while the peripheral atoms are the most electronegative.

4- Acids and bases

"… the definition of an acid and a base as a substance that loses or gains hydrogen ions is more general than what we have previously used…" (Lewis, 1923; cited by Jensen, 1995. Own translation).

5- Lewis's definition of acids and bases

“… A basic substance is one that has a pair of electrons that can be used to complete another atom and stabilize it (…). An acid substance is one that can use the pair of electrons from another molecule to complete and stabilize itself… ”(Lewis, 1923; cited by Jensen, 1995. Own translation).

6- The importance of hydrogen bonds

“… It seems to me that the most important addition to my theory of valences lies in what is known as hydrogen bonds (…) which means that a hydrogen atom can be bonded to two pairs of electrons from two different atoms, so it acts as a bridge between these two atoms… ”(Lewis, 1923; cited by Jensen, 1995. Own translation).

7- The valence electrons are those that allow the chemical bond to occur

Valence electrons are understood to be those found in the outermost shell of the atom.

8- The octet rule

Atoms with two or more electron shells have a tendency to lose, gain, or share electrons until their outermost shell is made up of eight valence electrons. Thus, the atoms gain their stability.

The other revolutions of chemistry

William B. Jensen (1995) points out that the history of modern chemistry is organized in a model composed of three revolutions, which correspond to three levels of the discourse of employees in today's chemistry. These three levels are:

1- The macroscopic level or molar level (simple substances, compounds, solutions and heterogeneous mixtures).

2- The atomic - molecular level (atoms, ions and molecules).

3- The subatomic level or electrical level (electrons and nuclei).

These three levels correspond to three different revolutions in chemistry:

1- The first revolution in chemistry occurred between 1770 and 1790

It allowed to clarify the concepts of simple substances and compounds, the role of heat and the conservation of mass in changes of state and chemical reactions.

To a large extent, this first revolution was the result of the works of the Frenchman Antoine Lavoisier.

2- The second revolution in chemistry occurred between 1855 and 1875

In this period, the atomic weights, the formulas of the molecular composition, the concept of valence and the periodic law were determined.

In this case, the revolution in chemistry was due to the work of many scientists, including the Italian Stanislao Cannizzaro, Williamson, Frankland, Odling, Wurtz, Couper, Kekulé, among others.

3- The third revolution happened between 1904 and 1924

It gave way to the modern electronic theory of chemical bonds and reaction. This revolution was the product of the interaction between physicists and chemists.

References

1. The Traité of the Third Chemical Revolution. A tribute to «Valence and the Structure of Atoms and Molecules. Retrieved on May 3, 2017, from che.uc.edu.
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5. The Chemical Revolution in the History of Chemestry. Retrieved on May 3, 2017, from jstor.org.
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