Rules for Writing & Evaluating Resonance Structures 1 Rule #1: No first-row element (C, N, O, etc.) can have > 8 electrons in its valence shell. H can only share 2 valence electrons. Rule #2: Resonance structures in which all atoms have a full octet (i.e. share 8 valence electrons) are lower in energy than those in which atoms are electron-deficient. is better than Rule #3: If there are electron deficiencies, these should preferably be on electropositive elements (e.g. B, C) not electronegative elements (e.g. O, N). Other factors that stabilize positive charge also help. is better than Rule #4: Resonance structures with charge separation are higher in energy than those where charge is neutralized. is better than Rule #5: If charge is separated, then electronegative elements should preferably have the negative charge, and electropositive elements should have the positive charge. is better than Chemistry 335 Supplemental Slides: Chapter 1

Hybridization & Frontier Molecular Orbital Theory 2 Chemistry 335 Supplemental Slides: Chapter 1

Hybridization & Frontier Molecular Orbital Theory 3 Chemistry 335 Supplemental Slides: Chapter 1

Hybridization & Frontier Molecular Orbital Theory 4 Chemistry 335 Supplemental Slides: Chapter 1

Hybridization & Frontier Molecular Orbital Theory 5 We can use these hybrid orbitals to explain bonding, shape, and lots of other properties! Chemistry 335 Supplemental Slides: Chapter 1

Hybridization & Frontier Molecular Orbital Theory 6 To create an orbital picture for ethane, we first combine an sp3-hybridized carbon atom with three hydrogens, to make a methyl radical... Chemistry 335 Supplemental Slides: Chapter 1

Hybridization & Frontier Molecular Orbital Theory 7 ... and then we combine two methyl radicals to generate a not-totally-accurate (but still very useful!) model of the electronic structure of ethane. Chemistry 335 Supplemental Slides: Chapter 1

Hybridization & Frontier Molecular Orbital Theory 8 To create an analogous picture for ethene (ethylene), we combine an sp2-hybridized carbon atom with two hydrogens... Chemistry 335 Supplemental Slides: Chapter 1

Hybridization & Frontier Molecular Orbital Theory 9 ... and then combine two fragments to generate a not-totally-accurate (but still very useful!) model of the electronic structure of ethene. Chemistry 335 Supplemental Slides: Chapter 1

Molecular Orbitals for Benzene 10 Chemistry 335 Supplemental Slides: Chapter 1