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pauling-Nobel_lecture1954 - LINUS PAULING Modern structural...

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L I N U S P A U L I N G Modern structural chemistry Nobel Lecture, December 11, 1954 A century ago the structural theory of organic chemistry was developed. Frankland in 1852 suggested that an atom of an element has a definite capacity for combining with atoms of other elements - a definite valence. Six years later Kekulé and Couper, independently, introduced the idea of valence bonds between atoms, including bonds between two carbon atoms, and suggested that carbon is quadrivalent. In 1861 Butlerov, making use for the first time of the term "chemical structure", stated clearly that the properties of a compound are determined by its molecular structure, and reflect the way in which atoms are bonded to one another in the molecules of the com- pound. The development of the structure theory of organic chemistry then progressed rapidly, and this theory has been of inestimable value in aiding organic chemists to interpret their experimental results and to plan new experiments. A most important early addition to organic structure theory was made by the first Nobel Laureate in Chemistry, Van ‘t Hoff, who in 1874 rec- ognized that the optical activity of carbon compounds can be explained by the postulate that the four-valence bonds of the carbon atom are directed in space toward the corners of a tetrahedron. The structure theory of inorganic chemistry may be said to have been born only fifty years ago, when Werner, Nobel Laureate in Chemistry in 1913, found that the chemical composition and properties of complex in- organic substances could be explained by assuming that metal atoms often coordinate about themselves a number of atoms different from their valence, usually four atoms at the corners either of a tetrahedron or of a square co- planar with the central atom, or six atoms at the comers of an octahedron. His ideas about the geometry of inorganic complexes were completely veri- fied twenty years later, through the application of the technique of X-ray diffraction. After the discovery of the electron many efforts were made to develop an electronic theory of the chemical bond. A great contribution was made in 1916 by Gilbert Newton Lewis, who proposed that the chemical bond,
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430 1 9 5 4 L . P A U L I N G such as the single bond between two carbon atoms or a carbon atom and a hydrogen atom represented by a line in the customary structural formula for ethane, consists of a pair of electrons held jointly by the two atoms that are bonded together. Lewis also suggested that atoms tend to assume the electronic configuration of a noble gas, through the sharing of electrons with other atoms or through electron transfer, and that the eight outermost elec- trons in an atom with a noble-gas electronic structure are arranged tetra- hedrally in pairs about the atom. Applications of the theory and additional contributions were made by many chemists, including Irving Langmuir and Nevil Vincent Sidgwick.
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