Lec-17-Chap-08-3

Lec-17-Chap-08-3 - CHE 131 Lecture 17, 2/28/2007 Lecture...

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CHE 131 Lecture 17, 2/28/2007 1 Lecture 17 Formal Charges (8.8) Resonance (8.9) Exceptions to the Octet Rule (8.10) Aromatic Compounds (8.11) Lecture 17: Knowledge and Skills Determine formal charges Recognize when resonance structures are needed Estimate the relative importance of resonance structures Estimate the consequences of resonance structures on bond lengths and charge distribution Write Lewis structures that do not follow the octet rule Recognize which elements are more likely to violate the oct. r. Explain the special stability of benzene Explain the difference in reactivity between benzene and alkenes Recognize the possibility of isomers in substituted benzenes Formal Charge It is the charge an atom would have, if all of the shared electrons were equally shared. It is the difference between the number of valence electrons on the free atom and the number of valence electrons assigned to the atom in the molecule . A A A A 2 L S C V F ⎛⎞ =− + ⎜⎟ ⎝⎠ O 4 2 4 6 FC + The Principle of Formal Charge H B H H H N H H H C H H H : + H + H + : H N H H H H B H H H + Isoelectronic series B 3( 08 / 2 ) 1 FC =−+ = C 4( / 2 )0 FC = N 5( / 2 FC =− + = +
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Lec-17-Chap-08-3 - CHE 131 Lecture 17, 2/28/2007 Lecture...

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