Ideas of Quantum Chemistry P45 shows how quantum mechanics is applied to chemistry to give it a theoretical foundation. The structure of the book (a TREE-form) emphasizes the logical relationships between various topics, facts and methods. It shows the reader which parts of the text are needed for understanding specific aspects of the subject matter. Interspersed throughout the text are short biographies of key scientists and their contributions to the development of the field. | 406 8. Electronic Motion in the Mean Field Atoms and Molecules Table . The dimensions of the electron pairs . 3 r2 . for CH3OH and CH3SH according to Core means the 1s orbital of the atom indicated CH3OH CH3SH core O core S 1s core C core C S L shell CO CS CH1b CH1b CH2 CH2 3b OH SH lone pair1 2c lone pair1 2c . Csizmadia in Localization and Delocalization in Quantum Chemistry ed. by O. Chalvet and R. Daudel D. Reidel Publ. Co. Dordrecht 1975. bDifferent electron pair dimensions originate from their different positions vs the OH or SH group. cThere are two lone pairs in the molecule. similar to the compounds of oxygen with hydrogen because sulphur and oxygen have analogous electronic configuration of the valence electrons . those of the highest energies and they differ only in the inner shells O He 2s22p4 as compared to S Ne 3s23p4 . Take a look of Table . Note that 1. The dimension of the electron lone pair localized on the 1s orbital of the sulphur atom is twice as small as the dimension of a similar pair of the 1s orbital of the oxygen atom. Nothing special. The electrons occupying the 1s orbital of S experience a strong electric field of the nucleus charged 16 while the charge of the O nucleus is only 8. Let us note that the core of the carbon atom is even larger because it is controlled by an even less charged nucleus124 6 . 2. The dimension of the electron pair of the 1s orbital of the carbon atom core C for CH3OH is very similar to that of the corresponding orbital for CH3SH vs .125 This means that the influence of the S atom as compared to the oxygen atom on the 1s orbital of the neighbouring atom is small. The local character of the interactions is thus the most decisive. 3. The influence of the S and O atoms on the CH bonds of the methyl group is only slightly larger. For example in CH3OH one of the CH bond
