CH301 - chapter 8 notes

CH301 - chapter 8 notes - 1 CH 301 Chapter 8 Molecular...

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1 CH 301 Chapter 8 Molecular Structure and Covalent Theories The material in this chapter will be covered as presented in this reading assignment, which is not necessarily in the same order as presented in the text. Valence Shell Electron Pair Repulsion Theory (VSEPR) Predicts the 3-D spatial arrangement of the atoms in polyatomic molecules and polyatomic ions. The spatial arrangement will be predicted from the regions of high electron density located around the central atom. The regions of high electron densities around the central atom will be arranged in order that the repulsions are as small as possible. The predicted spatial geometry of the atoms in a polyatomic molecule or polyatomic ion is called the electronic geometry . Rules to assigning regions of high electron densities around the central atom of a polyatomic molecule or polyatomic ion: 1. Bonds are counted as one region of high electron density. A single bond counts as one region of high electron density. A double bond counts as one region of high electron density. A triple bond counts as one region of high electron density. 2. Each lone pair (each unshared pair) of electrons counts as one region of high electron density. Table 8-1 – Describes the bond angles and electronic geometries associated with the different numbers of high electron densities around a central atom: You should become vary familiar with the above table!
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2 A Summary of Electronic Geometry Determination: Regions of high e density around the central atom Predicted bond angles Predicted shape of molecule 2 180 o linear 3 120 o trigonal planar 4 109.5 o tetrahedral 5 90 o , 120 o , 180 o trigonal bipyramidal 6 90 o , 180 o octahedral
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3 Valence Bond Theory Describes how bonding occurs Two atoms overlap valence electron orbitals to create a new set of lower energy orbitals that are shared between the two atoms. The new lower energy orbitals are called hybrid orbitals. The process of creating these new lower energy hybrid orbitals is called hybridization. Regions of high e density Electronic geometry Valence shell orbitals overlap of the central atom Hybridization 2 linear s and p sp 3 tri.planar s and 2 p’s sp 2 4 tetrahedral s and 3 p’s sp 3 5 tri. bipyramidal s, 3p’s, & d sp 3 d 6 octahedral s, 3p’s, & 2 d’s sp 3 d 2
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This note was uploaded on 06/19/2008 for the course CH 301 taught by Professor Fakhreddine/lyon during the Spring '07 term at University of Texas at Austin.

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CH301 - chapter 8 notes - 1 CH 301 Chapter 8 Molecular...

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