CHE_106_Lecture21_2009

CHE_106_Lecture21_2009 - Chemistry 106 Lecture 21 Topics:...

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Chemistry 106 Lecture 21 Topics: Molecular Shapes ESPR odel VESPR Model Text Reading: 9.1-9.4
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Bond Theory In this chapter we will discuss the geometries of molecules in terms of their electronic structure. – We will also explore two theories of chemical bonding: valence bond theory and molecular orbital theory . Molecular geometry is the general shape of a molecule, as determined by the relative positions of the atomic nuclei.
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Molecular Shape The shape of molecules is critical to their function. Shape is important in both small (e.g. Vitamin C) and large (e.g. proteins) molecules. C 2952 H 4664 N 812 O 832 S 8 Fe 4 Hemoglobin C 6 H 8 O 6 Vitamin C
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Molecular Shapes The shape of a molecule plays an important role in its reactivity. By noting the number of bonding and nonbonding electron pairs we can easily predict the shape of the molecule.
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Molecular Models of BF 3 and PF 3 BF 3 and PF 3 have the same atom count, but why different shapes?
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What Determines the Shape of a Molecule? Electron pairs, whether they be bonding or nonbonding, repel each other. By assuming the electron pairs are placed as far as possible from each other, we can predict the shape of the molecule.
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Electron Domains (Regions) We can refer to the electron pairs as electron domains or regions . In a double or triple bond, all electrons shared between those two atoms are on the same side of the central atom; therefore, they count as one electron domain. The central atom in this molecule, A, has four electron domains.
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Valence Shell Electron Pair Repulsion Theory (VSEPR) The best arrangement of a given number of electron omains is the one that domains is the one that minimizes the repulsions among them.
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The Valence-Shell Electron Pair Repulsion (VSEPR) Model The valence-shell electron pair repulsion (VSEPR) model predicts the shapes of molecules and ions by assuming that the valence shell electron pairs are arranged as far from one another as possible . – To predict the relative positions of atoms around a given atom using the VSEPR model, you first note the arrangement of the electron pairs around that central atom.
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The following rules and figures will help determine electron pair arrangements. 1. Draw the Lewis structure 2. Determine how many electron regions are around the central atom. Count a multiple bond as one region. Consider these as electron “domains”. 3. Arrange the electrons domains as shown in
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This note was uploaded on 02/09/2010 for the course CHE CHE 106 taught by Professor Korter during the Fall '09 term at Syracuse.

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CHE_106_Lecture21_2009 - Chemistry 106 Lecture 21 Topics:...

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