Chem111 Fall, 2005 51Lewis Dot Structures accounting of all of the valence electrons – where do they go?•1916, Gilbert Lewis bond involves a pairof electrons±"shared" by the atoms ±why 2? why not 1 or 3 or 7? Lewis derives a simple method for predicting bonding in molecules Octet Rule: atoms want to have/share 8 electrons in their valence (outer) shells ±accounts for a wide range of stable molecules ±lots of exceptions ±manifestation of the stability of the inert/noble gas e- configuration ±F ±F- and Ca ±Ca2+because of this! Examples.Let's get back to CO2and H2O … why does CO2have double bonds but H2O only has single bonds? H2O each H contributes 1 valence e- = 2 e- the O contributes 6 valence e- = 6 e-Total valence e- = 8 e- first, draw the molecule in its bonding arrangement HOHthen put in the bonding electrons – 2 per bond – leaves 8-4=4 e- to distribute HOHthen put in the remaining 4 electrons … HOHLecture 14: Bonding and Molecules•Lewis Dot Structures •VSEPR (I&II) ** see the Lewis Dot Structure Handout! ** two O-H single bonds
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