Abegg's rule

In chemistry, Abegg’s rule states that the difference between the maximum positive and negative valence of an element is frequently eight. The rule used a historic meaning of valence which resembles the modern concept of oxidation state in which an atom is an electron donor or receiver. Abegg’s rule is sometimes referred to as "Abegg’s law of valence and countervalence". In general, for a given chemical element (as sulfur) Abegg’s rule states that the sum of the absolute value of its negative valence (such as −2 for sulfur in H2S and its positive valence of maximum value (as +6 for sulfur in H2SO4) is often equal to 8. The concept was formulated in 1904 by German chemist Richard Abegg. Gilbert N. Lewis was one of the first to refer to the concept as "Abegg's rule" when he used it as a basis of argument in a 1916 article to develop his cubical atom theory, which developed into the octet rule. That article helped inspire Linus Pauling to write his 1938 textbook The Nature of the Chemical Bond.

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Cubical atom

The cubical atom was an early atomic model in which electrons were positioned at the eight corners of a cube in a non-polar atom or molecule. This theory was developed in 1902 by Gilbert N. Lewis and published in 1916 in the article "The Atom and the Molecule" and used to account for the phenomenon of valency. Lewis' theory was based on Abegg's rule. It was further developed in 1919 by Irving Langmuir as the cubical octet atom. The figure below shows structural representations for elements of the second row of the periodic table.

Valence (chemistry)

In chemistry, the valence (US spelling) or valency (British spelling) of an atom is a measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Different sources specify different definitions, but valence is generally understood to be the number of chemical bonds that each atom of a given element typically forms; for a specified compound the valence of an atom is the number of bonds formed by that atom. Double bonds are considered to be two bonds, and triple bonds to be three.

Valence bond theory

In chemistry, valence bond (VB) theory is one of the two basic theories, along with molecular orbital (MO) theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds when a molecule is formed. In contrast, molecular orbital theory has orbitals that cover the whole molecule. In 1916, G. N. Lewis proposed that a chemical bond forms by the interaction of two shared bonding electrons, with the representation of molecules as Lewis structures.

CH-160(en): Advanced general chemistry (english)

This course aims to teach essential notions of the structure of matter, chemical equilibria and reactivity. Classes and exercises provide the means to analyze and solve, by reasoning and calculation,

Introduces the basic concepts of organic chemistry and their practical applications in various industries and everyday life.

Delves into resonance in molecules, focusing on electron stabilization and reactivity through delocalization.

Explores the stability of isomers, Lewis acids and bases, and nucleophiles and electrophiles in chemical reactions.