Ch14_complete_062211 - Chapter #14 - Covalent Bonding:...

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Chapter #14 - Covalent Bonding: Orbitals 14.1 Hybridization and the Localized Electron Model 14.2 The Molecular Orbital Model 14.3 Bonding in Homonuclear Diatomic Molecules 14.4 Bonding in Heteronuclear Diatomic Molecules 14.5 Combining the Localized Electron and Molecular Orbital Models 14.6 Orbitals: Human Inventions 14.7-14.11: Spectroscopy (will not be covered this quarter)
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Hybridization and the Localized Electron Model Chapter 12: Atomic orbitals, Properties of electrons, Wave functions, Electronic configurations, Aufbau principle, etc. Chapter 13: General Concepts of Bonding in Molecules - Types of bonds: ionic, covalent, etc. - Bond energies, lengths, polarities, etc. Localized Electron Model - Lewis dot structures - Resonance structures - The octet rule - VSEPR model Chapter 14: What types of orbitals are used to form bonds?
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Valence Bond Theory Basic Principle of Localized Electron Model: A covalent bond forms when the orbitals from two atoms overlap and a pair of electrons occupies the region between the two nuclei. Rule 1: Maximum overlap. The bond strength depends on the attraction of nuclei to the shared electrons, so: The greater the orbital overlap, the stronger the bond.
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Valence Bond Theory Basic Principle of Localized Electron Model: A covalent bond forms when the orbitals from two atoms overlap and a pair of electrons occupies the region between the two nuclei. Rule 2: Spins pair. The two electrons in the overlap region occupy the same space and therefore must have opposite spins. There may be no more than 2 electrons in a molecular orbital.
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Valence Bond Theory Basic Principle of Localized Electron Model: A covalent bond forms when the orbitals from two atoms overlap and a pair of electrons occupies the region between the two nuclei. Rule 3: Hybridization. To explain experimental observations, Pauling proposed that the valence atomic orbitals in a molecule are different from those in the isolated atoms. We call this concept Hybridization
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What is hybridization? Atoms adjust to meet the “needs” of the molecule. In a molecule, electrons rearrange in an attempt to give each atom a noble gas configuration and to minimize electron repulsion . Atoms in a molecule adjust their orbitals through hybridization in order for the molecule to have a structure with minimum energy. The source of the valence electrons is not as important as where they are needed in the molecule to achieve a maximum stability.
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Example: Methane 4 equivalent C-H covalent bonds VSEPR predicts a tetrahedral geometry
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The Valence Orbitals of a Carbon Atom Carbon: 2s 2 2p 2 How do we explain formation of 4 equivalent C-H bonds?
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Hybridization: Mixing of Atomic Orbitals to form New Orbitals for Bonding + + + + + + +
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Other Representations of Hybridization: y 1 = 1/2[(2s) + (2p x ) + (2p y ) + (2p z )] y 2 = 1/2[(2s) + (2p x ) - (2p y ) - (2p z )] y 3 = 1/2[(2s) - (2p x ) + (2p y ) - (2p z )] y 4 = 1/2[(2s) - (2p x ) - (2p y ) + (2p z )]
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Hybridization is related to the number of valence electron pairs determined from VSEPR: Methane (CH 4 ) VSEPR: AB 4 tetrahedral sp 3 hybridized 109.47 º Electron pair geometry determines hybridization, not vice versa!!
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Ch14_complete_062211 - Chapter #14 - Covalent Bonding:...

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