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Chapter 11

CHEM 110 Chapter 11 Smart Notes.pdf

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Department
Chemistry
Course
CHEM 110
Professor
Bryan Sanctuary
Semester
Fall

Description
CHEM 110 Chapter 11 Smart Notes October, 2011 CHEM 110 Chapter 11 Smart Notes  11.1: What a Bonding Theory Should Do o When the potential energy reaches its lowest value, the two H atoms combine into a H2 molecule through a covalent bond. CHEM 110 Chapter 11 Smart Notes October, 2011 The inter-nuclear distance corresponds to the bond length. The potential energy corresponds to the negative of the bond-dissociation energy. CHEM 110 Chapter 11 Smart Notes October, 2011  11.2: Introduction to the Valence-Bond Method o Valence-Bond Method  Definition  A description of covalent bond formation in terms of atomic orbital overlap (interpenetration of two orbitals). CHEM 110 Chapter 11 Smart Notes October, 2011  Valence-Bond Method  Draw valence-shell orbital diagrams for the separate atoms.  Sketch the orbitals of the central atom that is involved in the overlap.  Complete the structure by bringing together the bonded atoms and representing the orbital overlap.  Describe the structure. CHEM 110 Chapter 11 Smart Notes October, 2011 o VSEPR Theory  Application  Can be used to explain the geometry of molecules  Limitation  Doesn’t describe the actual bonding and orbitals involved o Basic Valence Bond Theory  Application  Can be used to explain the bonding of molecules  Limitation  Doesn’t describe the geometry of molecules CHEM 110 Chapter 11 Smart Notes October, 2011  11.3: Hybridization of Atomic Orbitals o Hybridization  Definition  This is a mathematical process of replacing pure atomic orbitals with reformulated atomic orbitals for bonded atoms.  Hybridization occurs only when the bonds are being formed. o Hybrid Orbitals  Definition  New orbitals  The number of hybrid orbitals equals the total number of atomic orbitals that are combined. o Types of Orbitals  Hybrid Orbitals  Definition o This is one of the four orbitals formed by the hybridization of one s and three p orbitals. The angle between any two of the orbitals is the tetrahedral angle – 109.5 degrees.  Diagram on next page CHEM 110 Chapter 11 Smart Notes October, 2011 CHEM 110 Chapter 11 Smart Notes October, 2011 Hybridization of The bond angle is 107.5 CHEM 110 Chapter 11 Smart Notes October, 2011 Hybridization of The bond angle is 104.5 CHEM 110 Chapter 11 Smart Notes October, 2011  Hybrid Orbitals  The hybridization scheme corresponds to Trigonal-planar electron-group geometry and 120 bond angles. CHEM 110 Chapter 11 Smart Notes October, 2011  Hybrid Orbitals  The sp hybridization scheme corresponds to linear electron- group geometry and a 180 bond angle.  and Hybrid Orbitals CHEM 110 Chapter 11 Smart Notes October, 2011 o We can choose the likely hybridization scheme for a central atom in a structure in the valence bond method by  Writing a plausible Lewis Structure for the species of interest  Using VSEPR theory to predict the probably electron group geometry of the central atom  Selecting the hybridization scheme corresponding to the electron group geometry CHEM 110 Chapter 11 Smart Notes October, 2011 CHEM 110 Chapter 11 Smart Notes October, 2011  11.4: Multiple Covalent Bonds o Bonds  Sigma Bond  Orbitals that overlap in this end-to-end fashion produce a sigma bond, designated bond.  Pi Bond  The bond produced by a side-to-side overlap of two parallel orbitals is called a pi bond, designated by abond.  NOTE: That only one of the bonds in a multiple bond is a bond; the others are bonds – one pi bond in a double bond and two in a triple bond. CHEM 110 Chapter 11 Smart Notes October, 2011  11.5: Molecular Orbital Theory o Molecular Orbital Theory  Definition  Describes the covalent bonds in a molecule by replacing atomic orbitals of the component atoms by molecular orbitals belonging to the molecule as a whole. A set of rules is used to assign electrons to these molecular orbitals, thereby yielding the electronic structure of the molecule. o Molecular Orbitals  Definition  A series of orbitals that belong to the molecule as a whole.  Molecular orbitals are mathematical functions, but we can relate them to the probability of finding electrons in certain regions of a molecule.  A molecular orbital can accommodate just two electrons, and the electrons must have opposing spins.  Bonding  Greater probability of finding the electron between the nuclei  The increased electron charge density between the nuclei causes them to draw closer together to form a chemical bond and reduces repulsions between the positively charged nuclei and promotes a strong bond.  The result of this constructive interference is a bonding molecular orbital because it places a high CHEM 110 Chapter 11 Smart Notes October, 2011 electron charge density between the two nuclei. CHEM 110 Chapter 11 Smart Notes October, 2011  Antibonding  Leads to reduced electron probability between the nuclei, which produces an antibonding molecular orbital(*), because it places a very low electron charge density between the two
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