CHEM 012 7

5 check the structure by councng valence electrons

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Unformatted text preview: Now add an octet to all EXCEPT the central atom O C O Now how many valence electrons have been used? 3.  Is this structure complete? (check that all valence electrons have been used, and that each element has the proper number of electrons (an octet for all but H and He) CreaCng Double Bonds In the structure for CO2, all the valence electrons have been used but C does not have an octet. What do we do? EACH oxygen will generously share a pair of electrons with the carbon. Remember that a pair of O C O electrons is a bond. O C O VERIFY that each atom has an octet, and that the proper number of valence electrons are present! 10 9/29/11 Other MulCple Bonds Consider the molecule N2 (this is the form in which nitrogen is found in the air around us) 1.  How many valence electrons are there? 2.  If the skeleton of the molecule is N- N, how can we draw the Lewis diagram? N N N N All valence electrons have been used, but neither N has an octet. We can share pairs of electrons as before. But here, we must share an electron pair from each N instead of just one. So N2 has a “triple bond” in its structure Checklist for Drawing Lewis Structures 1.  Using the Periodic Table, determine the total number of valence electrons in the structure. 2.  Draw the skeleton structure, and subtract two electrons for each bond formed 3.  Use remaining valence electrons to create octets on all atoms except the central atom (if there is one) 4.  If valence electrons are used up and some atoms don’t have octets, use double and/or triple bonds to create octets. 5.  CHECK t...
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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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