CHEM 012 7

5 hepwwwelmhursteduchmvchembook204tetrahedralhtml

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Unformatted text preview: he structure by counCng valence electrons (remember each individual bond = 2 electrons) 11 9/29/11 Ozone •  How do we draw the Lewis structure for ozone? •  Three oxygen atoms so a total of 18 valence electrons •  “Skeleton” uses four electrons, leaving 14 to create octets: O O O O O O But the central oxygen does not have an octet… Ozone •  One of the “end” oxygen’s can share an extra pair with the central oxygen. •  But which one? –  IT DOESN’T MATTER O O O O O O These are called resonance structures and both are required to fully specify the Lewis structure of ozone. They are needed when there is a choice of where to place a double bond. 12 9/29/11 Resonance Structures •  Resonance structures, such as those seen in O3, are not intended to imply that there are two structures rapidly switching back and forth. •  Instead, the “real” structure is viewed as a blend of all the resonance structures that can be drawn for the species. •  So ozone, having resonance structures with one double bond and one single bond, could be viewed as having 1.5 bonds between the central oxygen and each terminal oxygen Shapes of Molecules •  Lewis structure do not tell us the actual three- dimensional shape of the molecule. However, a correct Lewis structure will allow us to predict the shape of a molecule. •  Molecular shapes are based on the fact that electron pairs repel each other, so they want to be as far apart as possible. 13 9/29/11 Methane Consider methane… Its Lewis structure is: This Lewis structure may lead you to believe that methane is flat, with 90° angles between the electron...
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This note was uploaded on 09/06/2012 for the course CHEM 012 taught by Professor M.lester during the Fall '12 term at UPenn.

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