Laws of affinityThis is a featured page

In chemistry, the laws of affinity are any of various combining theories or rules for how specific chemical species can combine according to affinity preferences or necessities. [1]

In the history of chemistry, there have been at least a dozen or more laws of affinity, depending on which chemist is sourced. One of the first, was Greek philosopher Plato's c. 390 BC affinity law that "like tends towards like". Over the years, these affinity laws became more elaborate and complex as new chemical discoveries occurred.

The first "affinity table" was made in 1718 by French physician and chemist Étienne Geoffroy. Geoffroy's first law of affinity was that:

“Whenever two substances are united that have a disposition to combine and a third is added that has a greater affinity with one of them, these two will unite, and drive out the other.”

To expound on this law, using data from the 1718 edition of Newton's Opticks (query 31), Geoffroy made a sixteen-column, eight-row, affinity containing twenty-four reacting species, showing specifically what affinity reactions would occur between various combinations of reactants.


Short history
In circa 450 BC, Greek philosopher Empedocles’ introduced his "standard model" of physics, in which the universe was comprised of four elements: fire (θ∆ics - Encyclopedia of Humanthermodynamics), earth (θ∆ics - Encyclopedia of Humanthermodynamics), air (θ∆ics - Encyclopedia of Humanthermodynamics), water (θ∆ics - Encyclopedia of Humanthermodynamics), meaning that humans are entities made of four elements, whose interactions were governed by two forces: philia (●→|←●), i.e. attraction (or love) and neikos (←●|●→), i.e. repulsion (or hate). In short, two forces governed movement: philia (attractive force) and neikos (repulsive force). Empedocles expanded on this via employing anthropomorphized types of chemical aphorisms: as in enemies repel; friends attract.

In c. 390 BC, Greek philosopher Plato built on Empedocles’ conception of philia (attractive force) and neikos (repulsive force) by postulating the first law of affinity that “likes tend toward likes” (likes attract), e.g. earth to earth or water to water, etc.

In 1250, Albertus Magnus applied the conception of ‘affinity’ to chemical systems and postulated four laws of affinity. [2]


In 1687, English physicist Isaac Newton proposed that chemical affinities were due to certain forces that would likely follow similar laws analogous to the three laws of planetary motion. He expanded on these views in ‘Query 31’ of his 1704 Opticks. In 1718, after translating Newton’s Opticks, French physician and chemist Étienne Geoffroy proposed a new law of affinity that ‘whenever two substances are united that have a disposition to combine and a third is added that has a greater affinity with one of them, these two will unite, and drive out the other.’ Using this law, he published the first every affinity table.

In 1749, building on Geoffroy’s affinity table, French chemist J. P. Macquer published six truths of chemical affinity, which encompassed both Plato’s and Geoffroy’s affinity laws, as well as four new ones. In 1766, he published seven types of affinity in his Dictionnaire de chymie. In this direction, most consider Isaac Newton to be the one who stimulated the discovery of the "laws of attraction". Before this, however, the ancient Greeks knew from magnetic interactions that "opposites attract" and "likes repel". This factor is modeled, in modern terms, via Coulomb's law.

In the latter half of the 20th century, the theory of electromagnetism, unified by Scottish physicist James Clerk Maxwell in 1873, is the physics of the electromagnetic field; a field encompassing all of space which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. This effect, as modeled via Maxwell's field equations, can be thought of as the electromagnetic laws of attraction and repulsion.

With the discovery of sub-atomic particles, such as the quark (1964), and the fundamental forces, the term "laws of attraction" has been replaced with the conception of field particle exchange, and the bonding effect created therefrom. Subsequently, in the 20th century the laws of affinity were replaced by the laws of quantum chemistry and chemical thermodynamics.

In the mid 20th century, social scientists began to apply Plato's first law of affinity, i.e. "likes attract", to relationship life noting that, for example, people tend to marry based on such factors as age, religion, socioeconomic status, and education. In the 1950s, in opposition to this view, sociologist Robert Winch proposed the "opposites attract" theory, arguing that people are attracted to those whose needs conversely match his or her own. [3]

References
1. Kim, Mi Gyung. (2003). Affinity, That Elusive Dream – A Genealogy of the Chemical Revolution. Cambridge, Mass: The MIT Press.
2. Magnus, Albertus. (c. 1250). The Book of Secrets (1999 reprint). York Beach, Maine: Samuel Weiser, Inc.
3. Hoffman, Edward; Weiner, B., Marcella (2003). The Love Compatibility Book. New World Library.

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