1057_RG_2_08 - Chem 1057 J. Walcott CEN TER FOR LEARNIN G...

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Chem 1057 CENTER FOR LEARNING AND TEACHING J. Walcott LEARNING STRATEGIES CENTER Fall 2008 Review Guide #2 Lecture: 9/1/08 – 9/5/08: Chapter 1 I. Lewis Structures and Formal Charges Please refer to Review Guide #1 for the general procedure for writing Lewis structures and for calculating formal charges on atoms. II. Molecular Shapes/Bonding A. VSEPR theory 1. From the Lewis structures with single, double or triple bonds, we can predict bond angles using the VSEPR (valence-shell electron-pair repulsion) model. According to the VSEPR model, the outer shell valence electrons may form single, double or triple bonds, or they may be unshared. Each situation creates a negatively charged region of space. Because like charges repel each other, the regions of electron density around an atom spread so that each is as far away from the others as possible. Using the VSEPR model the shape of the molecule can be predicted. B. Hybridization To account for the observed bond angles in covalent bonds with second-period elements (carbons, nitrogen and oxygen), atomic orbitals combine to form new orbitals, called hybrid orbitals. The number of hybrid orbitals formed is equal to the number of atomic orbitals combined. Elements of the second period form three types of hybrid orbitals, designated sp 3 , sp 2 and sp. 1. Bond length: The length of the sigma bond depends upon the amount of s (or p) character in the bond. An sp 3 sigma bond is longer than an sp 2 bond which is longer than an sp bond. Generally, shorter bonds are stronger bonds. 2.
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1057_RG_2_08 - Chem 1057 J. Walcott CEN TER FOR LEARNIN G...

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