introduced the concept of electronegativity in 1932. Using the various properties of molecules, such as the energy required to break bonds and the dipole moments of molecules, he established a scale and an associated numerical value for most of the elementsthe Pauling Electronegativity Scalewhich is useful in predicting the nature of bonds between atoms in molecules. In 1936, Pauling was promoted to Chairman of the Division of Chemistry and Chemical Engineering at Caltech, and to the position of Director of the Gates and Crellin laboratories of Chemistry. He would hold both positions until 1958. Pauling also spent a year in 1948 at the University of Oxford as George Eastman Visiting Professor and Fellow of Balliol. Nature of the chemical bond In the late 1920s, Pauling began publishing papers on the nature of the chemical bond. Between 1937 and 1938, he took a position as George Fischer Baker Non-Resident Lecturer in Chemistry at Cornell University. While at Cornell, he delivered a series of nineteen lectures and completed the bulk of his famous textbook The Nature of the Chemical Bond. 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's book has been considered "chemistry's most influential book of this century and its effective bible". In the 30 years after its first edition was published in 1939, the book was cited more than 16,000 times. Even today, many modern scientific papers and articles in important journals cite this work, more than seventy years after the first publication. 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 and p, 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 (mathematically) 'mixed' or 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