Chemical affinity

Last updated

In chemical physics and physical chemistry, chemical affinity is the electronic property by which dissimilar chemical species are capable of forming chemical compounds. [1] Chemical affinity can also refer to the tendency of an atom or compound to combine by chemical reaction with atoms or compounds of unlike composition.

Contents

History

Early theories

The idea of affinity is extremely old. Many attempts have been made at identifying its origins. [2] The majority of such attempts, however, except in a general manner, end in futility since "affinities" lie at the basis of all magic, thereby pre-dating science. [3] Physical chemistry, however, was one of the first branches of science to study and formulate a "theory of affinity". The name affinitas was first used in the sense of chemical relation by German philosopher Albertus Magnus near the year 1250. Later, those as Robert Boyle, John Mayow, Johann Glauber, Isaac Newton, and Georg Stahl put forward ideas on elective affinity in attempts to explain how heat is evolved during combustion reactions. [4]

The term affinity has been used figuratively since c. 1600 in discussions of structural relationships in chemistry, philology, etc., and reference to "natural attraction" is from 1616. "Chemical affinity", historically, has referred to the "force" that causes chemical reactions. [5] as well as, more generally, and earlier, the ″tendency to combine″ of any pair of substances. The broad definition, used generally throughout history, is that chemical affinity is that whereby substances enter into or resist decomposition. [2]

The modern term chemical affinity is a somewhat modified variation of its eighteenth-century precursor "elective affinity" or elective attractions, a term that was used by the 18th century chemistry lecturer William Cullen. [6] Whether Cullen coined the phrase is not clear, but his usage seems to predate most others, although it rapidly became widespread across Europe, and was used in particular by the Swedish chemist Torbern Olof Bergman throughout his book De attractionibus electivis (1775). Affinity theories were used in one way or another by most chemists from around the middle of the 18th century into the 19th century to explain and organise the different combinations into which substances could enter and from which they could be retrieved. [7] [8] Antoine Lavoisier, in his famed 1789 Traité Élémentaire de Chimie (Elements of Chemistry), refers to Bergman's work and discusses the concept of elective affinities or attractions.

According to chemistry historian Henry Leicester, the influential 1923 textbook Thermodynamics and the Free Energy of Chemical Reactions by Gilbert N. Lewis and Merle Randall led to the replacement of the term "affinity" by the term "free energy" in much of the English-speaking world.

According to Prigogine, [9] the term was introduced and developed by Théophile de Donder. [10]

Goethe used the concept in his novel Elective Affinities (1809).

Visual representations

The affinity concept was very closely linked to the visual representation of substances on a table. The first-ever affinity table, which was based on displacement reactions, was published in 1718 by the French chemist Étienne François Geoffroy. Geoffroy's name is best known in connection with these tables of "affinities" (tables des rapports), which were first presented to the French Academy of Sciences in 1718 and 1720, as shown below:

Geoffroy's Affinity Table (1718): At the head of the column is a substance with which all the substances below can combine, where each column below the header is ranked by degrees of "affinity". Affinity-table.jpg
Geoffroy's Affinity Table (1718): At the head of the column is a substance with which all the substances below can combine, where each column below the header is ranked by degrees of "affinity".

During the 18th century many versions of the table were proposed with leading chemists like Torbern Bergman in Sweden and Joseph Black in Scotland adapting it to accommodate new chemical discoveries. All the tables were essentially lists, prepared by collating observations on the actions of substances one upon another, showing the varying degrees of affinity exhibited by analogous bodies for different reagents.

Crucially, the table was the central graphic tool used to teach chemistry to students and its visual arrangement was often combined with other kinds diagrams. Joseph Black, for example, used the table in combination with chiastic and circlet diagrams to visualise the core principles of chemical affinity. [11] Affinity tables were used throughout Europe until the early 19th century when they were displaced by affinity concepts introduced by Claude Berthollet.

Modern conceptions

In chemical physics and physical chemistry, chemical affinity is the electronic property by which dissimilar chemical species are capable of forming chemical compounds. [1] Chemical affinity can also refer to the tendency of an atom or compound to combine by chemical reaction with atoms or compounds of unlike composition.

In modern terms, we relate affinity to the phenomenon whereby certain atoms or molecules have the tendency to aggregate or bond. For example, in the 1919 book Chemistry of Human Life physician George W. Carey states that, "Health depends on a proper amount of iron phosphate Fe3(PO4)2 in the blood, for the molecules of this salt have chemical affinity for oxygen and carry it to all parts of the organism." In this antiquated context, chemical affinity is sometimes found synonymous with the term "magnetic attraction". Many writings, up until about 1925, also refer to a "law of chemical affinity".

Ilya Prigogine summarized the concept of affinity, saying, "All chemical reactions drive the system to a state of equilibrium in which the affinities of the reactions vanish."

Thermodynamics

The present IUPAC definition is that affinity A is the negative partial derivative of Gibbs free energy G with respect to extent of reaction ξ at constant pressure and temperature. [12] That is,

It follows that affinity is positive for spontaneous reactions.

In 1923, the Belgian mathematician and physicist Théophile de Donder derived a relation between affinity and the Gibbs free energy of a chemical reaction. Through a series of derivations, de Donder showed that if we consider a mixture of chemical species with the possibility of chemical reaction, it can be proven that the following relation holds:

With the writings of Théophile de Donder as precedent, Ilya Prigogine and Defay in Chemical Thermodynamics (1954) defined chemical affinity as the rate of change of the uncompensated heat of reaction Q' as the reaction progress variable or reaction extent ξ grows infinitesimally:

This definition is useful for quantifying the factors responsible both for the state of equilibrium systems (where A = 0), and for changes of state of non-equilibrium systems (where A ≠ 0).

See also

Notes

  1. 1 2 Chisholm 1911 , Affinity, Chemical
  2. 1 2 Levere, Trevor, H. (1971). Affinity and Matter – Elements of Chemical Philosophy 1800-1865. Gordon and Breach Science Publishers. ISBN   2-88124-583-8.
  3. Malthauf, R. P. (1966). The Origins of Chemistry. Pg. 299. London.
  4. Partington, J.R. (1937). A Short History of Chemistry. New York: Dover Publications, Inc. ISBN   0-486-65977-1
  5. Thomas Thomson. (1831). A System of Chemistry, vol. 1. p.31 (chemical affinity is described as an "unknown force"). 7th ed., 2 vols.
  6. See Arthur Donovan, Philosophical Chemistry in the Scottish Enlightenment, Edinburgh, 1975
  7. Eddy, Matthew Daniel (2004). "Elements, Principles and the Narrative of Affinity". Foundations of Chemistry: 161–175.
  8. On the variety of affinity theories, see Georgette Taylor, Variations on a Theme; Patterns of Congruence and Divergence among 18th Century Affinity Theories, VDM Verlag Dr Muller Aktiengesellschaft, 2008
  9. I.Prigogine. (1980). From being to becoming. Time and Complexity in the Physical Sciences. San Francisco: W.H.Freeman and Co
  10. de Donder, T. (1936). L'affinité. Ed. Pierre Van Rysselberghe. Paris: Gauthier-Villars
  11. Eddy, Matthew Daniel (2014). "How to See a Diagram: A Visual Anthropology of Chemical Affinity". Osiris. 29: 178–196. doi:10.1086/678093.
  12. IUPAC Green Book and Gold Book in .pdf

Related Research Articles

Chemistry scientific discipline

Chemistry is the scientific discipline involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.

Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurements of various thermodynamic properties, but also the application of mathematical methods to the study of chemical questions and the spontaneity of processes.

Thermodynamic free energy

The thermodynamic free energy is a concept useful in the thermodynamics of chemical or thermal processes in engineering and science. The change in the free energy is the maximum amount of work that a thermodynamic system can perform in a process at constant temperature, and its sign indicates whether a process is thermodynamically favorable or forbidden. Since free energy usually contains potential energy, it is not absolute but depends on the choice of a zero point. Therefore, only relative free energy values, or changes in free energy, are physically meaningful.

Redox Chemical reaction

Redox is a type of chemical reaction in which the oxidation states of atoms are changed. Redox reactions are characterized by the transfer of electrons between chemical species, most often with one species undergoing oxidation while another species undergoes reduction. The chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. In other words:

In chemistry, the amount of substance in a given sample of matter is the number of discrete atomic-scale particles in it divided by the Avogadro constant. The particles or entities may be molecules, atoms, ions, electrons, or other, depending on the context. The value of the Avogadro constant NA has been set to 6.02214076×1023 mol−1. The amount of substance is sometimes referred to as the chemical amount.

Torbern Bergman Swedish chemist

Torbern Olaf (Olof) Bergman (KVO) was a Swedish chemist and mineralogist noted for his 1775 Dissertation on Elective Attractions, containing the largest chemical affinity tables ever published. Bergman was the first chemist to use the A, B, C, etc., system of notation for chemical species.

Étienne François Geoffroy French chemist

Étienne François Geoffroy was a French physician and chemist, best known for his 1718 affinity tables. He first contemplated a career as an apothecary, but then decided to practice medicine. He is sometimes known as Geoffroy the Elder.

<i>Elective Affinities</i> novel by Johann Wolfgang von Goethe

Elective Affinities, also translated under the title Kindred by Choice, is the third novel by Johann Wolfgang von Goethe, published in 1809. The title is taken from a scientific term once used to describe the tendency of chemical species to combine with certain substances or species in preference to others. The novel is based on the metaphor of human passions being governed or regulated by the laws of chemical affinity, and examines whether or not the science and laws of chemistry undermine or uphold the institution of marriage, as well as other human social relations.

The philosophy of chemistry considers the methodology and underlying assumptions of the science of chemistry. It is explored by philosophers, chemists, and philosopher-chemist teams. For much of its history, philosophy of science has been dominated by the philosophy of physics, but the philosophical questions that arise from chemistry have received increasing attention since the latter part of the 20th century.

History of chemistry Wikimedia history article

The history of chemistry represents a time span from ancient history to the present. By 1000 BC, civilizations used technologies that would eventually form the basis of the various branches of chemistry. Examples include extracting metals from ores, making pottery and glazes, fermenting beer and wine, extracting chemicals from plants for medicine and perfume, rendering fat into soap, making glass, and making alloys like bronze.

In chemistry, the valence or valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. The concept of valence was developed in the second half of the 19th century and helped successfully explain the molecular structure of inorganic and organic compounds. The quest for the underlying causes of valence led to the modern theories of chemical bonding, including the cubical atom (1902), Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958), and all of the advanced methods of quantum chemistry.

Chemism refers to forces of attraction or adhesion between entities. It has uses in chemistry and philosophy.

Merle Randall was an American physical chemist famous for his work with Gilbert N. Lewis, over a period of 25 years, in measuring reaction heat of chemical compounds and determining their corresponding free energy. Together, their 1923 textbook "Thermodynamics and the Free Energy of Chemical Substances" became a classic work in the field of chemical thermodynamics.

In the history of science, the principle of maximum work was a postulate concerning the relationship between chemical reactions, heat evolution, and the potential work produced there from. The principle was developed in approximate form in 1875 by French chemist Marcellin Berthelot, in the field of thermochemistry, and then later in 1876 by American mathematical physicist Willard Gibbs, in the field of thermodynamics, in a more accurate form. Berthelot's version was essentially: "every pure chemical reaction is accompanied by evolution of heat.". The effects of irreversibility, however, showed this version to be incorrect. This was rectified, in thermodynamics, by incorporating the concept of entropy.

Théophile de Donder Belgian physicist

Théophile Ernest de Donder was a Belgian mathematician and physicist famous for his work in developing correlations between the Newtonian concept of chemical affinity and the Gibbsian concept of free energy.

History of molecular theory

In chemistry, the history of molecular theory traces the origins of the concept or idea of the existence of strong chemical bonds between two or more atoms.

Chemical substance matter of constant composition best characterized by the entities (molecules, formula units, atoms) it is composed of

A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or alloys. Chemical elements may or may not be included in the definition, depending on expert viewpoint.

This glossary of chemistry terms is a list of terms and definitions relevant to chemistry, including chemical laws, diagrams and formulae, laboratory tools, glassware, and equipment. Chemistry is a physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions; it has an extensive vocabulary and a significant amount of jargon.

Chemical compound Substance composed of multiple elements

A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. Two atoms of the same element bonded in a molecule do not form a chemical compound, since this would require two different elements.

References