Chapter9 - 11/2/2011 1 1 CHEMISTRY 1307 CHEMISTRY 1307...

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Unformatted text preview: 11/2/2011 1 1 CHEMISTRY 1307 CHEMISTRY 1307 Chapter IX Bonding and Molecular Structure: Orbital Hybridization and Molecular Orbitals 2 Advanced Theories of Chemical Bonding 1) _______________Theory 2) _______________Theory Atomic Atomic Orbitals Molecules 3 Valence Bonding Theory Developed by Linus Pauling Premise: Bonding involves valence electrons. Half-filled atomic orbitals on bonding atoms overlap to form bonds. Bonds are localized between atoms (or as lone pairs). Leads to prediction of molecular shape. Linus Pauling, 1901-1994 11/2/2011 2 4 Valence Bond Theory The main points of the valence bond approach to bonding are: Orbitals overlap to form a bond between two atoms. Overlapping orbitals hold two electrons of opposite spin. Usually, one electron is supplied by each of the two bonded atoms. The bonding electrons are localized with a higher probability of being found within a region of space between the bonding nuclei. Both electrons are simultaneously associated with both nuclei. 5 Valence Bond Terminology overlap: two orbitals existing in the same region of space lp: lone pair of electrons (non-bonding) bp: bonding pair of electrons (result of orbital overlap) central atom: the atom of concern in a molecule hybridization: the linear combination of atomic orbitals hybrid orbital: bonding orbitals that arise from the mixing of AO s. -bond: (sigma bond) overlap of orbitals along the bond axis -bond: (pi bond) overlap of orbitals above and below the bond axis. single bond: one -bond double bond: one -bond & one -bond triple bond: one -bond & two -bonds 6 The Orbital Overlap Model of Bonding A _______ bond is defined as a bond in which electron density lies along the axis of the bond. In H 2 a sigma ( ) covalent bond that arises from the overlap of two half filled s orbitals, one from each atom. 11/2/2011 3 7 Sigma Bond Formation Two __ orbitals overlap Overlap of an ____ orbital Two ___ orbitals overlap 8 Sigma ( ) Bonding When bonding occurs along a bond axis, it is referred to as a _____ bond: ( ) The electrons occupy space between the nuclei. 9 Pi ( ) Bonding Pi bonds ( bonds) are covalent chemical bonds where two lobes of one atomic orbital overlap two lobes of the other atomic orbital. The electrons occupy space ______ and ______ the nuclei. 11/2/2011 4 10 Hybridization of Atomic Orbitals The simple model of atomic orbital overlap in H 2 , HF and F 2 breaks down for more complicated molecules. Consider methane: VSEPR theory predicts bond angles of ______ . These angles can t be achieved with the s, p x , p y & p z orbitals of the central carbon atoms. 11 Hybridization of Atomic Orbitals In order to attain the needed geometry, the atomic orbitals (AO s) mix or _________ to form new valence bond orbitals....
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This note was uploaded on 11/18/2011 for the course CHEM 1307 taught by Professor Li during the Fall '08 term at Texas Tech.

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Chapter9 - 11/2/2011 1 1 CHEMISTRY 1307 CHEMISTRY 1307...

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