7 junio, 2024

Third chemical revolution: what it is, origin, ideas, characters

What is the third revolution of chemistry?

The third revolution of chemistry refers to the advances that were made in the area of ​​this branch of science in the 20th century, specifically between 1904 and 1924. Some of these were the delimitation of the concept of valence, the contributions of Lewis in terms of atomic configurations, the covalent bonds, acids and bases, electronegativity and hydrogen bonding.

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

Main ideas of the third revolution of chemistry

On valence and the structure of atoms and moleculesthe work of Gilbert N. Lewis, is the source of many of the current ideas in electronic theory about bonding and reactivity.

It was the key work of the third chemical revolution. Some of the most relevant contributions of this document are the following, taken verbatim from the aforementioned work (those in quotes):

1. The bond formed through a shared pair of electrons

«… the chemical bond is, at all times and in all molecules, a pair of electrons that remain together…».

2. Link continuity 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 end, according to the environmental conditions. However, this does not happen per saltumbut that it occurs through imperceptible gradations…”.

3. The relationship between bond polarity and electronegativity

“…the pair of electrons constituting the bond can be 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…”.

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 used previously [por ejemplo, las definiciones de Arrhenius] …”.

5. The Lewis 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…”.

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 attached to two pairs of electrons from two different atoms , so it acts as a bridge between these two atoms…”.

7. Valence electrons are what allow the chemical bond to occur

Valence electrons are 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.

Characters of the third chemical revolution and their contributions

gilbert newton lewis (1875-1946), American physical chemist who devised the concept of covalent bonding and coined the term «photon.» Also, he established the octet rule.

Niels Bohr (1885-1962), Danish physicist who helped to understand the atom and quantum mechanics.

– Henry Moseley (1887-1915), British physical chemist who discovered 5 new elements and established the concept of atomic number.

Erwin Schrödinger (1887-1961), Austrian physicist who established the «Schrödinger equation», which would become the foundation of quantum mechanics.

Werner Heisenberg (1901-1976), German theoretical physicist, pioneer of quantum mechanics.

Linus Pauling (1901-1994), American chemical engineer and biochemist. Among other contributions, he introduced the valence bond theory. He was one of the first quantum chemists.

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 discourse used in chemistry today. 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 distinct revolutions in chemistry:

1. First revolution in chemistry: between 1770 and 1790

It allowed to clarify the concepts of simple and compound substances, 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 work of the Frenchman Antoine Lavoisier.

2. The second revolution in chemistry: between 1855 and 1875

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

In this case, the chemistry revolution 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 in chemistry: 1904 and 1924

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


The Treaty of the Third Chemical Revolution. A tribute to “Valence and the Structure of Atoms and Molecules. Retrieved from che.uc.edu.
The Chemical Revolution. Retrieved from acs.org.

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