In chemistry, history of chemical bonding theory traces the development of the various theories of how atoms bond to each other to form molecules and how molecules and other chemical species chemically bond to each other to form larger structures, all attached via chemical bonds.

The following timeline traces the development of chemical bonding theory over the years.

Bonding Model

c.450BCAtomic theoryLeucippus 75Leucippus
(c.500-450 BC)
Supposed that the universe consists of only atoms and voids; may have speculated on how the atoms hold together to form larger mass.
c.410BCHook-and-eye atomic attachmentDemocritus 75Democritus
(c.460-370 BC)
Argued that atoms of solids were hooked and so stuck to one another. In order to make the solid hard, however, the atoms must not only be hooked, but retain their hooked shape when they come into contact with other atoms. [1]Hooked atoms
c.75BCHook-and-eye atomic attachmentLucretius 75Lucretius (99-55 BC)“Things which look to us hard (diamonds, basalt blocks, iron, brass bolts) and close-textured must consist of atoms that are hooked together, and must be held in union, because welded together through and through out of atoms that are, as it were, many-branched.” Liquids are, as rule, formed of smooth and round elements, but sluggish fluid, like oil, may have its atoms: “larger or more hooked and intertangled” than those of wine.
Nicolas Lemery 75Nicolas Lemery
The spike of an acid fit into the grove or inlet of a base to yield a less abrasive product.Acid and Alkali

Person?"Glued together by rest"

Person?"Stuck together by conspiring motions"
(chemical affinity)
Isaac Newton (75px)Isaac Newton "Particles attract one another by some force, which in immediate contact is exceedingly strong, at small distances performs the chemical operations, and reaches not far from the particles with any sensible effect."
1757Crotchet symbol
(bonding bracket)
Cullen 75William Cullen
“By the mark { I mean them united to another.” [4]Bracket
Roger Boscovich 75Roger Boscovich (1711-1787)At short range, atoms attracted each other, but at longer range atoms pushed each other way. [5]
Bergman 75Torbern Bergman
Pioneered the use of letters, a, b, c, etc., to represent unattached chemicals and adjacent letters, e.g. ab or ac, to represent chemical "union" in the context of before and after aspects of affinity reactions.
AB (union)
1789Divided force theoryphoto needed 75 William Higgins (1763-1825) Theory: the strength of the force between two ultimate particles [atoms] should be divided accordingly. If the force between the ultimate particle of oxygen and the ultimate particle of nitrogen were 6, for instance, than the nitrogen and oxygen would each be assigned a force component of 3. [6]Higgins molecules
1810Ball-and-stick model
John Dalton
In 1810, Dalton had his Peter Ewart make a set of wooden balls, shown adjacent, of different sizes, that could be connected via metal pins and holes in each ball, so to demonstrate his newly "atomic theory".Dalton's wooden ball atomic model (1810)
1852Combining power
Edward Frankland 75 Edward Frankland (1825-1899)Explained that each element has a certain combining power.
1858Single bondsArchibald Couper 75Archibald Couper (1831-1892) Extrapolated ideas on elective affinity attractions between atoms to formulate a chemical bonding theory; was the first to use was the first to use lines between atoms, in conjunction with the older method of using brackets. [13]
A-B (union)
1861Double bonds
Triple bonds
Loschmidt 75Josef Loschmidt
Originated the use of double lines and triple lines to represent double bonds and triple bonds, respectively, in molecules. [2]Loschmidt (molecules2)
Edward Frankland 75Edward Frankland
“The bracket has been employed in various senses in chemical formulae; but I now propose to restrict its use to one purpose only, namely for expressing chemical combination between two or more elements which are placed perpendictularly with regard to each other and next to the bracket in a formula. No. I. signifies that two atoms of carbon are directly united with each other; No. II. That two atoms of carbon are linked, as it were, together by an atom of oxygten, the latter beign united to both carbon atoms; No. III. Expresses the fact that one atom of oxygen in the formula of the upper line is linked to another atom of oxygen in the formula of the lower line by the atom of barium.” Frankland 1877 bonding bracket examples
1898Sensitive region overlapBoltzmann 75Ludwig Boltzmann (1844-1906)“When two atoms are situated so that their sensitive regions are in contact, or partly overlap, will there be a chemical attraction between them. We then say that they are chemically bound to each other.” Two iodine atoms, A and B, each represented by a region of size M, attached at their sensitive regions, α and β; which must exist owing to ‘the facts of chemical valence’. Boltzmann sensitive region overlap
1902Electron dot structure
(shared electrons)
Gilbert Lewis 75Gilbert Lewis
Cubit atoms bonding at electron corners to form chemically bonded cubit molecules, in such a matter that each atom finds the most stability when it satisfies "Abegg's law of valence" (atomic shells filled with eight electrons are especially stable atoms). Lewis cubit atoms
Fritz Haber 75Fritz Haber (1868-1934)“These cases are generally explained by assuming the breaking of weak, but ‘real’, bonds between the phosphorus tricholoride and chlorine, the hydrochloric acid and the ammonia, and between he carbamic acid and the ammonia. When such an assumption does not agree with the current conception of valence, as in the case of acetic acid, which, like nitric oxide, shows a marked tendency to polymerize just above the boiling point, ‘molecular compounds’ are assume.”
Fritz Haber (1905), Thermodynamics of Technical Gas Reaction (pg. 154)

1913Shared electrons
(shell overlap)
Gilbert Lewis 75Gilbert Lewis“Two atoms may conform to the rule of eight, or the octet rule, not only by the transfer of electrons from one atom to another, but also by sharing one or more pairs of electrons. Two electrons thus coupled together, when lying between two atomic centers, and held jointly in the shells of the two atoms, I have considered to be the chemical bond.”Lewis chemical bond

1917Hooked atomsNote: the Dalton-version of the "hook-and-eye bonding method" was still being taught at Oregon Agricultural College (to Linus Pauling); the teaching of this archaic method is what supposedly drove Pauling to write the now famous 1939 textbook On The Nature of the Chemical Bond.
1923Lewis commented: “Two atoms may conform to the rule of eight, or the octet rule, not only by the transfer of electrons from one atom to another, but also by sharing one or more pairs of electrons. Two electrons thus coupled together, when lying between two atomic centers, and held jointly in the shells of the two atoms, I have considered to be the chemical bond. We thus have a concrete picture of that physical entity, that ‘hook and eye’ which is part of the creed of the organic chemist.” (Valence and the Structure of Atoms and Molecules)

Quantum mechanical bonding

1927Heitler-London theoryWalter Heitler 75Walter Heitler
Using Niels Bohr’s model of the atom, Louis de Broglie’s electron wave theory, and Erwin Schrödinger’s wave equation, conceptualized the idea that the movements of the electrons, technically called electron wavefunctions (mathematical expressions involving the coordinates of the electrons in space) can join together mathematically with plus, minus, and exchange terms, to form a Lewis-type covalent bond.Exchange force

(exchange interaction model)
(exchange force)

Fritz London 75Fritz London
(co-theorist with Heitler)
1927Valence bond theory

c. 1932Hybrid bond orbitalsPauling 75Linus Pauling
[12]Sp3 hybrid orbitals

1933Orbital overlap model of bonding

bonding molecular orbitals
antibonding molecular orbitals

Chemical thermodynamic bonding

1941Bond energyFritz Lipmann 75Fritz Lipmann
In his “Metabolic Generation and Utilization of Phosphate Bond Energy”, using Lewis thermodynamics (1923), he introduced the notion of "bond energy", according to which energy is stored in the three high-energy phosphate bonds, each on the magnitude of 20 kJ of free energy per bond per mol, amounting to about 55 kJ per mole of ATP; energy which acts as a kind of storage fuel or battery that can be used later to drive typical endergonic reactionsATP
1999Thermodynamic theory of bindingJulie Forman-Kay 75Julie Forman-Kay
“Whether two molecules will bind is determined by the free energy change (ΔG) of the interaction, composed of both enthalpic (H) and entropic (S) terms.”[9]

Human chemical bonding
In 1995, American electrochemical engineer Libb Thims began to work on the problem of how’s and why’s of the method by which free energy actuates to predict the feasibility of human reproduction reactions (child formation), the core aspect of mate selection, modeling each person as a chemical entity, using Bergman chemical symbol notation, as follows:

M + F → C

according to the view that if one can measure the free energy of the reacting system in the initial state (M + F), say the year the couple first meet, and the free energy of the reacting system in the final state (C), say the year in which the child becomes an adult and leaves the confines of the parental home, the entire reaction can thus be predetermined as functionable or not according to the spontaneity criterion. In circa 2002, however, Thims arrived at the view (see: Thims history) that in his calculations he was neglecting the stored bond energy, in the Lipmann sense (above), of free energy associated with the tightly formed parental bond structure M≡F at the point of the child departure, say at 18-year mark into the reaction; hence the following newly-conceived human reproduction reaction mechanism quickly came to the fore, as a type of glass wall problem:

M + F → MF + C

The problem of nature of the “human chemical bond”, symbol MF or M≡F, arose from the quagmire a very-large yet unsolved, let alone completely unaddressed, problem to be tackled. It took nearly seven years to get a handle on this human chemical bond “≡” problem, as outlined below, which involved an assimilation of the above historical models, into a working model to explain the phenomenon of the (electromagnetic force) bonding of human molecules (people):

2003Human molecular orbital theoryThims 75 newLibb Thims
Developed the concept of the ‘human molecular orbital’ (modeled on standard molecular orbital theory), in which the 90 percent probability region of a person's location over the surface of the earth, the person considered as a human particle, is satellite-tracked and traced into that of common ‘activity orbitals’, wherein each person is shown inside of American anthropologist Edward Hall's 1996 conception of 'reaction bubbles' (a type of personal space), according to which the probability region boundary is defined as one's thermodynamic boundary. Bonding begins to occur when common ‘activity orbitals’ overlap and in which reaction bubble interaction occurs. Human molecular orbital
2004Field particle exchange theory
Libb ThimsUsing particle physics logic, developed the model that a bond holds owing the actions of an exchange force, in which the exchange of field particles carries and transmits the force: "when attraction, related to field-particle exchange, outweighs repulsion, related to field-particle exchange, then those ‘attached’ matter-particles [ô], as humans, are held in place—as if an apparent ‘bond’ were in existence."
Human  chemical bond diagram (energy view)
2005Human chemical bond
Libb Thims Began to incorporate turning tendencies (1885), Gottman stability ratios (1994), and Feynman diagram models, photon-electron sensory stimulus descriptions, etc., into a more robust human bonding model as outlined in the unfinished JHT article "On the Nature of the Human Chemical Bond." Feynman diagram interaction
2007Dodecabond model
Libb ThimsBegan to blend evolutionary psychology into chemical thermodynamics arguments, defining human bonding in terms of specific enthalpic ties and entropic ties, devoting nearly half the 2007 textbook Human Chemistry, to a unified model of human chemical bonding. [10]Dodecabond model

1. Franklin, James. (1986). “Are Dispositions Reducible to Categorical Properties?” (abstract), The Philosophical Quarterly, 36: 62-64.
2. Loschmidt, Joseph. (1861). Chemische Studien: Constitutions-Formeln der organischen Chemie in graphischer Darstellung : Das Mariott'sche Gesetz (Chemical studies: Constitutions formulas of organic chemistry in graphical representation: The Act Mariott'sche). Gerold.
3. Masson, John. (1907). Lucretius, Epicurean and Poet (hooked atoms, pg. 92-93, 107). Dutton.
4. Crosland, M. P. (1959). “The use of diagrams as chemical ‘equations’ in the lecture notes of William Cullen and Joseph Black.” Annals of Science, Vol 15, Num 2, June.
5. Boscovich, Roger. (1763). Theoria Philosophiae Naturalis (Theory of Natural Philosophy). Publisher.
6. Higgins, William. (1789). A Comparative View of Phlogistic and Antiphlogistic Theories. J. Murray.
7. Boltzmann, Ludwig (1898). Lectures on Gas Theory (pg. 377). J. A. Barth.
8. Frankland, Edward. (1877). Experimental Researches in Pure, Applied and Physical Chemistry (the use of brackets in chemical formulae, pg. 11). J. Van Voorst.
9. Forman-Kay, Julie D. (1999). “The ‘Dynamics’ in the Thermodynamics of Binding.” Nature Structure Biology, 6: 1086-87.
10. Thims, Libb. (2007). Human Chemistry (Volume One) (human molecular orbtal, pg. 265; orbital transition state, pgs. 268-69). Morrisville, NC: LuLu.
12. Pauling, Linus. (1983). "The Development of the Concept of Chemical Bond." Hitchcock Foundation Lectures January 17, University of California, Berkeley.
13. (a) Couper, A.S. (1858). “On a New Chemical Theory”, Comptes Rendus de l’Academie des Sciences, 46: 1157; trans. in Alembic Club Reprint, No. 21. p. 9, and in Classics, (pg. 132).
(b) Benfey, Otto T. (1992). From Vital Force to Structural Formulas (pg. 88). Chemical Heritage Foundation.

Further reading
● Bantz, David A. (1980). “The Structure of Discovery: Evolution of Structural Accounts of Chemical Bonding”, in: Scientific Discovery: Case Studies (editor: Thomas Nickles) (pgs. 291-330). Taylor & Francis.

External links
Chemical bonding model – Wikipedia.

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