CHEM 1211 Lecture 22 Outline of Last Lecture I Clicker Questions A Clicker Question 1 B Clicker Question 2 C Clicker Question 3 II Bond Length Strength III Bond Strength IV Strengths of Covalent Bonds V Using Bond Dissociation Enthalpies VI Valence Bond Theory A VB Theory Analysis of BeCl2 Outline of Current Lecture I Ethene Double Bond II Ethyne Triple Bond III Molecualr Orbital Theory IV BO in MO V Excited States Current Lecture I Ethene Double Bond H H C C H H VSEPR Anaylysis Three regions around each carbon atom Trigonal Planar Valence Bond Theory Need three hybridized orbitals from C so we need 3 AOs 2s 2p C C C Two sp2 hybridized C atoms plus p orbitals in proper orientation II Ethyne Triple Bond H C C H III IV V VSEPR Analysis Linear two regions VB Theory Sp hybridization Molecualr Orbital Theory MO predicts electron pair spectra and paramagnetism MO VB Theory predict bond order MO only diatomic molecules two atoms bonded together When two wave fxn orbitals on different atoms act constructively they produce a new MO with double the amplitude instructive interference or no amplitude NODE destructive interference LCAO Linear combination of Atomic Orbitals When AO add a lower energy sigma bonding MO forms When AO subtract higher energy and anti bonging MOs form Anti bonding orbitals are designated by an asterisk BO in MO Bo of bonding electrons anti bonding electrons 2 Electrons in bonding molecular orbitals add stability Electrons in anti bonding molecular orbitals reduce stability Excited States What happens to a H2 molecule if one of the electrons is excited to the anti bonding orbital The molecules fall apart photodissociation
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