Linus Pauling and The Nature of the Chemical Bond: A Documentary History Narrative  
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Pauling, under the direction of major professor Roscoe Dickinson, had done his doctoral work on molecular structure: determining the architecture of molecules, the positions of atoms, the angles and distances between them, using a new technology called x-ray crystallography. It would form an important part of his approach to the chemical bond.

Almost all solids exist in crystalline forms, in which the atoms are arranged in repeating three-dimensional patterns. Some crystals, including those in many metals, are too small to be seen with the naked eye. Others, from table salt to emeralds, quartz to rock candy, can grow very large. But regardless of the crystal’s size, it was impossible to "see" the positions of the underlying atoms.

Until 1912, when Max Theodor Felix von Laue, a German physicist, discovered a roundabout way of seeing the unseeable. He did it by shooting a beam of x-rays at crystals and then analyzing the way the atoms in the crystal reflected the x-rays. The resulting "diffraction pattern" could be seen by developing a piece of photographic film placed near the crystal. By analyzing the pattern created by the scattered x-rays — a process requiring very complex mathematical calculations — researchers could painstakingly work out, at least for simple crystals, the distances and angles between the atoms that comprised them. Once the basic crystal unit involved more than a handful of atoms, however, the patterns became too complex to analyze directly.

Researchers had guessed at molecular structures for decades. But without any way to verify the guesses, they remained just that. X-ray crystallography was a fantastic tool. Caltech was one of the first places to use it in a comprehensive research program. And again, Pauling would lead the way.

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Audio Clip  Audio: The Influence of Roscoe Dickinson. 1977. (1:32) Transcript and More Information

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Video Clip  Video: Lecture 1, Part 9. 1957. (2:03) Transcript and More Information

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See Also: Translation of 'Remarks on the Apparent Selective Reflection of X-Rays in Crystals', W. Kossel, z. f. Phys., 23, 278 (1924). 1920s. 
See Also: "X-Ray Crystallography and the Nature of the Chemical Bond." April 18, 1991. 
See Also: "The Future of Physical Chemistry" May 7, 1968.  Clip: Determining Crystal Structures. (0:55)

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Portrait of Max Theodore Felix von Laue, approx. 1914.


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Laue X-Ray Photographs. October 31, 1922.

"I consider my entry into the field of x-ray crystallography, nine years after it had been developed, to be just about the most fortunate accident that I have experienced in my life."

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