Linus Pauling

Linus Carl Pauling (February 28, 1901 – August 19, 1994) was an American physical chemist, widely regarded as the premier chemist of the twentieth century. Pauling was a pioneer in the application of quantum mechanics to chemistry, and in 1954 was awarded the Nobel Prize in chemistry for his work describing the nature of chemical bonds. He also made important contributions to crystal and protein structure determination, and was one of the founders of molecular biology. Pauling received the Nobel Peace Prize in 1962 for his campaign against above-ground nuclear testing, becoming the only person in history to individually receive two Nobel Prizes (Marie Curie won Nobel Prizes in physics and chemistry, but shared the former and won the latter individually; John Bardeen won two Nobel Prizes, but both were in the field of physics, and both were shared; Frederick Sanger won two Nobel Prizes in chemistry, but one was shared). Later in life, he became an advocate for regular consumption of massive doses of Vitamin C, a regimen now regarded as medically unorthodox.

Work on the nature of the chemical bond

In the 1930s he began publishing papers on the nature of the chemical bond, leading to his famous textbook on the subject published in 1939. It is based primarily on his work in this area that he received the Nobel Prize in Chemistry in 1954 "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances". Pauling summarized his work on the chemical bond in The Nature of the Chemical Bond, a magnum opus which is probably the most influential chemistry book ever published. An idea of its importance can be gleaned from the fact that in the 30 years since its first edition was published in 1939, the book had been cited more than 16,000 times. Even today, it is remarkable how many modern scientific papers and articles in important journals cite this work, more than half a century after it was published.

Related Topics:
1930s - 1939 - Nobel Prize in Chemistry - 1954

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Part of Pauling's work on the nature of the chemical bond led to his introduction of the concept of orbital hybridization. While it is normal to think of the electrons in an atom as being described by orbitals of types such as s, p, etc., it turns out that in describing the bonding in molecules, it is better to construct functions that partake of some of the properties of each. Thus the one 2s and three 2p orbitals in a carbon atom can be combined to make four equivalent orbitals (called sp3 hybrid orbitals), which would be the appropriate orbitals to describe carbon compounds such as methane, or the 2s orbital may be combined with two of the 2p orbitals to make three equivalent orbitals (called sp2 hybrid orbitals), with the remaining 2p orbital unhybridized, which would be the appropriate orbitals to describe certain unsaturated carbon compounds such as ethylene. Other hybridization schemes are also found in other types of molecules.

Related Topics:
Orbital hybridization - Electron - Atom - Orbitals - Molecule - Carbon - Methane - Unsaturated - Ethylene

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Another area which he explored was the relationship between ionic bonding, where electrons are transferred between atoms, and covalent bonding where electrons are shared between atoms on an equal basis. Pauling showed that these were merely extremes, between which most actual cases of bonding fall. It was here especially that Pauling's electronegativity concept was particularly useful; the electronegativity difference between a pair of atoms will be the surest predictor of the degree of ionicity of the bond.

Related Topics:
Ionic bond - Electron - Atom - Covalent bond - Electronegativity

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The third of the topics that Pauling attacked under the overall heading of "the nature of the chemical bond" was the accounting of the structure of aromatic hydrocarbons, particularly the prototype, benzene. The best description of benzene had been made by the German chemist Friedrich Kekulé. He had treated it as a rapid interconversion between two structures, each with alternating single and double bonds, but with the double bonds of one structure in the locations where the single bonds were in the other. Pauling showed that a proper description based on quantum mechanics was an intermediate structure containing some aspects of each. The structure was a superposition of structures rather than a rapid interconversion between them. The name "resonance" was later applied to this phenomenon. In a sense, this phenomenon resembles that of hybridization, described earlier, because it involves combining more than one electronic structure to achieve an intermediate result.

Related Topics:
Aromatic hydrocarbon - Benzene - German - Friedrich Kekulé - Double bond - Quantum mechanics

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