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Unformatted text preview: 1 LewisStructures.wpd 7/29/99 Drawing Lewis Structures The fact that a plausible Lewis structure can be drawn for a species is NOT proof that this is the true electronic structure. Experimental verification is always required. Generalizations about Lewis Structures 1. All the valence electrons of the atoms in a Lewis structure must be accounted for. 2. Usually , each atom in a Lewis structure acquires an electron configuration with an outer-shell octet. (Hydrogen is limited to an outer-shell duet.) 3. Usually , all the electrons in a Lewis structure are paired. 4. Often , both atoms in a bonded pair contribute equal numbers of electrons to the covalent bond, but sometimes , both electrons in a bonded pair are derived from one atom. (Such a bond is referred to as a coordinate covalent bond.) 5. Sometimes , it is necessary use double or triple bonds in a Lewis structure. 6. Sometimes , it is possible to draw more than one plausible structure (for a given formula) where the constituent atoms are in physically different locations with respect to one another. In these instances the different structures represent different chemical entities. (These different entities are called ISOMERS .) 7. Sometimes , it is impossible to draw only one structure that is consistent with ALL of the available data (that is, with the constituent atoms in exactly the same positions). In these instances the true structure can only be represented as a composite or HYBRID of the two or more plausible structures. (This situation is called RESONANCE .) Strategies for Drawing Lewis Structures 1. Start with a plausible Skeleton structure. This is a representation of the order in which the atoms are bonded. The skeleton consists of one or more central atoms with other atoms (called terminal atoms) bonded to the central atom(s). Usually, the atom of lowest electronegativity is the central atom....
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