In existographies, Walter Heitler (19041981) (IQ:##) (GPE:48) (CR:11) was a German physicist noted, his 1927 article “Interaction of Neutral Atoms and Homopolar Bonding according to Quantum Mechanics”, coauthored with Fritz London (19001954), wherein they employed or synthesized used Niels Bohr's model of the atom (Bohr model), Louis de Broglie’s electron wave theory, and Erwin Schrödinger’s wave equation, to quantify and 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 Lewistype covalent bond, which by 1956 had solidified into the model that particles in their orbits have an "interaction energy" (aka exchange force) which actuates or realized the bond.


Overview
In 1927, Heitler, in his article “Interaction of Neutral Atoms and Homopolar Bonding according to Quantum Mechanics”, coauthored with Fritz London (19001954), used Danish physicist Niels Bohr's model of the atom (Bohr model), French physicist Louis de Broglie’s electron wave theory, and Austrian physicist Erwin Schrödinger’s wave equation, to quantify and 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 Lewistype covalent bond. [1] In short, they explained the interaction and bonding of atoms according to quantum mechanics, thus launching the subject of quantum chemistry.
In 1927, Heitler, in his article “Interaction of Neutral Atoms and Homopolar Bonding according to Quantum Mechanics”, coauthored with Fritz London (19001954), used Danish physicist Niels Bohr's model of the atom (Bohr model), French physicist Louis de Broglie’s electron wave theory, and Austrian physicist Erwin Schrödinger’s wave equation, to quantify and 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 Lewistype covalent bond. [1] In short, they explained the interaction and bonding of atoms according to quantum mechanics, thus launching the subject of quantum chemistry.
Terms such as bound state, binding energy, overlap integral, exchange energy, supposedly, all stem from this socalled HeitlerLondon theory. [2]
Heitler commented the following on his new quantum mechanical bonding model discovery, in retrospect: [3]
“I slept till very late in the morning, found I couldn’t do work at all, had a quick lunch, went to sleep again in the afternoon and slept until five o’clock. When I woke up...I had clearly...the picture before me of the two wave functions of two hydrogen molecules joined together with a plus and minus and with the exchange in it. So I was very excited, and I got up and thought it out. As soon as I was clear that the exchange did play a role, I called London up, and he came to me as quickly as possible. Meanwhile I had already started developing a sort of perturbation theory. We worked together then until rather late at night, and then by that time most of the paper was clear.... Well...at least it was not later than the following day that we had the formation of the hydrogen molecule in our hands, and we also knew that there was a second mode of interaction which meant repulsion between two hydrogen atoms, also new at the time—new to chemists, too.”
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Quotes  On
The following are quotes on Heitler:
“Neumann may have the greatest polymath in the 20th century, but he is certainly not one of the greatest physicists of the 20th century. Notably, his greatest contribution to physics was in development the mathematical foundations of quantum mechanics. When Von Neumann started working on quantum mechanics, the equations of quantum mechanics had already been derived, and the experiments had already been understood. What was lacking was the proof of the mathematical consistency of these equations. Von Neumann's work was brilliant in seeing the mathematical relationship between the, then, new equations of quantum mechanics, and other branches of mathematics, but this added nothing to the physical predictions and concepts developed by Dirac, Heitler, Pauling, Tomonaga, Fermi, Bethe, Heisenberg, Born, etc.”— Bosco (2008), Reddit post (Ѻ) to ‘Why is Neumann considered the greatest scientist of the last century?’
Quotes  By
The following are quotes by Heitler:
“My interest in science awoke rather early, at the age of 10 or 12 or so. I don’t think it was stimulated by a special home atmosphere or by school. My father was a professor for engineering, and so the atmosphere at home was certainly not unfavorable, but it did not particularly stimulate interest in science. I was first interested in astronomy; at the age of 12 or so I made myself a telescope from an old camera lens and the objective of an old microscope. I was very happy then that I could see the ring of Saturn and so on. Well, later at the age of 14 or 15 I became interested in practically everything scientific — mathematics, physics and chemistry, even geology. I installed a chemical laboratory in the bathroom which was perhaps not always to the pleasure of my family, and so on. My school education was mainly classic, Latin and Greek. And for this I’m very grateful, in fact. Especially, I derived a great deal of pleasure and interest from Greek — Greek philosophy, Greek poetry. Plato was my favorite philosopher, and perhaps he still is. The science, teaching in school was rather poor; my mathematics teacher was a kindly old man, but as I usually was far in advance of his lessons, I used the mathematics lessons for preparing the next Latin lesson or so, and he didn’t object. The physics teacher’s main concern was to be against Einstein and against relativity. Well, I was not on very good terms with him, or he was not with me, to put it more precisely, especially since he once discovered that I was reading a book by Einstein secretly under my desk.”— Walter Heitler (1963), “Interviewed by John Heilbron” (Ѻ), Mar 18
See also
● History of chemical bonding theory
References
1. Heitler, Walter and London, Fritz. (1927). “Interaction of neutral atoms and homopolar bond according to quantum mechanics” (“Wechselwirkung neutraler Atome and homoopolare Bindung nach der Quantenmechanik”), Zeitschift fur Physik, 44: 45572.
2. Bantz, David A. (1980). “The Structure of Discovery: Evolution of Structural Accounts of Chemical Bonding”, in: Scientific Discovery: Case Studies (editor: Thomas Nickles) (pgs. 291330). Taylor & Francis.
3. Heitler, Walter. (1963). “Article” (quote), AHQP (Archive for the History of Quantum Physics), volume 6. March 18.
External links
● Walter Heitler – Wikipedia.