Chapter2 - 2-2-1Structure and Structure and properties of...

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Unformatted text preview: 2-2-1Structure and Structure and properties of properties of organic organic moleculesmoleculesChapter 2Chapter 22-2-2Quantum or Wave MechanicsQuantum or Wave MechanicsAlbert Einstein: E = h(energy is quantized)light has particle propertiesLouis deBroglie: wave/particle dualityErwin Schrdinger: wave equationwave function, wave function, : a solution to a set of equations that depicts the energy of an electron in an atomeach wave function is associated with a unique set of quantum numberseach wave function occupies three-dimensional space and is called an orbitalorbital =hm2-2-3Shapes of 1Shapes of 1ssand 2and 2ssOrbitalsOrbitalsProbability distribution (2) for 1sand 2sorbitals showing an arbitrary boundary surface containing about 95% of the electron density2-2-4Shapes of a Set of 2Shapes of a Set of 2ppAtomic OrbitalsAtomic OrbitalsThree-dimensional shapes of 2patomic orbitals2-2-5Molecular Orbital TheoryMolecular Orbital TheoryElectrons in atoms exist in atomic orbitalsElectrons in molecules exist in molecular orbitals (MOs)Using the Schrdinger equation, we can calculate the shapes and energies of MOs2-2-6Molecular Orbital TheoryMolecular Orbital TheoryRules:combination of natomic orbitals (mathematically adding and subtracting wave functions) gives nMOs (new wave functions)MOs are arranged in order of increasing energyMO filling is governed by the same rules as for atomic orbitals:Aufbau principle: fill beginning with LUMO (lowest unoccupied molecular orbital)Pauli exclusion principle: no more than 2e-in a MOHunds rule: when two or more MOs of equivalent energy are available, add 1e-to each before filling any one of them with 2e-2-2-7Molecular Orbital TheoryMolecular Orbital TheoryTerminologyground state = lowest energy stateexcited state = NOT lowest energy state= sigma bonding MO* = sigma antibonding MO= pi bonding MO* = pi antibonding MOHOMO = highest occupied MOLUMO = lowest unoccupied MO2-2-8Molecular Orbital TheoryMolecular Orbital TheoryBonding of H2HH1sa1sbMOLECULAR ORBITAls2-2-9Molecular Orbital TheoryMolecular Orbital TheoryMO energy diagram for H2: (a) ground state and (b) lowest excited state2-2-1010Molecular OrbitalsMolecular Orbitalscomputed sigma bonding and antibonding MOs for H22-2-1111Molecular OrbitalsMolecular Orbitalspi bonding and antibonding MOs2-2-1212Molecular OrbitalsMolecular Orbitalscomputed pi bonding and antibonding MOs for ethylene2-2-1313Molecular OrbitalsMolecular Orbitalscomputed pi bonding and antibonding orbitals for formaldehyde2-2-1414Shapes of Molecules: VSEPRShapes of Molecules: VSEPRBased on the twin concepts thatatoms are surrounded by regions of electron densityregions of electron density repel each otherHCCHOCCHNHHCHHOHCHC HHO4 regions of e- density(tetrahedral, 109.5)3 regions of e- density(trigonal planar, 120)2 regions of e- density(linear, 180)HCHHHNHHH::::::::HHOCHN2-...
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This note was uploaded on 09/19/2011 for the course CHM 261 taught by Professor Wenthold during the Spring '11 term at Purdue University-West Lafayette.

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Chapter2 - 2-2-1Structure and Structure and properties of...

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