Molecular Structures I Compounds of Main Group Elements

8 Molecular Structures I Compounds of Main Group Elements 

Usually a molecule consists of atoms with different electronegativities, and the more electronegative atoms have smaller coordination numbers (we only count covalently bonded atoms as belonging to the coordination sphere of an atom). The more electronegative atoms normally fulfill the 8 —N rule in many cases they are terminal atoms , i.e. they have coordination number 1. Elements of the second period of the periodic table almost never surpass the coordination number 4 in molecules. However, for elements of higher periods this is quite common, the 8 - N rule being violated in this case. 

The structure of a molecule depends essentially on the covalent bond forces acting between its atoms. In the first place, they determine the constitution of the molecule, that is, the sequence of the linkage of the atoms. The constitution can be expressed in a simple way by means of the valence bond formula. For a given constitution the atoms arrange themselves in space according to certain principles. These include atoms not bonded directly with one another may not come too close (repulsion of interpenetrating electron shells) and the valence electron pairs of an atom keep as far apart as possible from each other. 

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MOLECULAR STRUCTURES I COMPOUNDS OF MAIN GROUP ELEMENTS... 

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