1A8and9PPT - Chemistry 1A Chapters 8 and 9 Molecular...

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Chemistry 1A Chapters 8 and 9
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Molecular Orbital Theory ± Goal: to generate molecular orbital diagrams that describe molecules, like the atomic orbital diagrams that describe atoms. ± Molecular Orbital: a volume within which a high percentage of the negative charge for an electron in a molecule is found.
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Atomic Orbitals and Molecular Orbitals
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Molecular Orbital Diagram for O 2 Like Atomic Orbital Diagram for O
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Goal: To determine the MO Diagram for Diatomic Molecules We assume that the electrons would fill the molecular orbitals of molecules like electrons fill atomic orbitals in atoms. The molecular orbitals are filled in a way that yields the lowest potential energy for the molecule. The maximum number of electrons in each molecular orbital is two. (We follow the Pauli exclusion principle.) Orbitals of equal energy are half filled with parallel spin before they begin to pair up. (We follow Hund's Rule.)
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Linear Combination of Atomic Orbitals - LCAO Atomic orbitals (AOs) of about the same energy overlap to form molecular orbitals (MOs). Pairs of AOs overlap in two extreme ways. In-phase to bonding MO out-of-phase to antibonding MO
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Electron and Light Waves is like Describes the variation in the intensity of negative charge created by an electron. Describes the variation in the electric and magnetic fields created by light.
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Wave Interference
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In-Phase and Out-of- Phase Interactions Light waves can interact in-phase and out-of-phase. In-phase leads to an increase in the intensity of the light (brighter). Out-of-phase leads to a decrease in the intensity of the light (less bright). Electron waves can interact in-phase and out-of-phase. In-phase leads to an increase in the intensity of the negative charge. Out-of-phase leads to a decrease in the intensity of the negative charge.
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MOs from 1s Orbitals
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Bonding Molecular Orbital From in-phase interaction of two atomic orbitals. Leads to an increase in negative charge between two nuclei where the atomic orbitals overlap. Leads to more +/- attraction between the negative charge generated by the electrons and the nuclei. Thus there is a decrease in PE. Energy would be required to separate the atoms, so electrons in this type of molecular orbital tend to keep atoms together.
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Antibonding Molecular Orbital From out-of-phase interaction of two atomic orbitals. Leads to a decrease in negative charge between two nuclei where the atomic orbitals overlap. Leads to less +/ attraction between the negative charge generated by the electrons and the nuclei. Thus there is an increase in PE. Electrons are more stable in separate atomic orbitals of separate atoms, so electrons in this type of molecular orbital tend to keep atoms separate.
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MOs from 1s Orbitals (cont.)
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Molecular Orbitals from 2p x Atomic Orbitals
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Molecular Orbitals from 2p y Atomic Orbitals
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Why σ 2p lower PE than π 2p ?
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1A8and9PPT - Chemistry 1A Chapters 8 and 9 Molecular...

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