CHEM 1211 Lecture 22Outline of Last Lecture I. Clicker QuestionsA. Clicker Question #1B. Clicker Question #2C. Clicker Question #3II. Bond Length/StrengthIII. Bond StrengthIV. Strengths of Covalent BondsV. Using Bond Dissociation EnthalpiesVI. Valence Bond TheoryA. VB Theory Analysis of BeCl2Outline of Current Lecture I. Ethene: Double BondII. Ethyne: Triple BondIII. Molecualr Orbital TheoryIV. BO in MOV. Excited StatesCurrent Lecture: I. Ethene: Double BondH H C=CH HVSEPR Anaylysis:- Three regions around each carbon atom - Trigonal PlanarValence Bond Theory:- Need three hybridized orbitals from C, so we need 3 AOs2s 2p C=C: C Two sp2 hybridized C atoms plus p orbitals in proper orientationII. Ethyne: Triple BondH – C = C – HVSEPR Analysis:- Linear, two regionsVB Theory:- Sp hybridizationIII. 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 (*)IV. 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 stabilityV. Excited States- What happens to a H2 molecule if one of the electrons is excited to the anti-bonding orbital? - The molecules fall apart:
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