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Chem121-Chapter-9-SH

Chem121-Chapter-9-SH - Chapter 9 Molecular Geometry and...

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1 Chapter 9 Molecular Geometry and Bonding Theories © 2009 R. Spinney Molecular Geometry The chemical reactivity of molecules depend on the 3D structure of the molecule as well as the nature of the bonds between atoms. Molecular geometry describes the positions of atoms in a molecule relative to one another. Ball and stick or space filling models are useful. Descriptive Shapes of Some AB n Molecules
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2 Shapes of AB n Molecules (cont’d) There are additional possible molecular geometries. For n = 2: For n = 3: For n = 4: For n = 5: How can the shape be predicted? VSEPR One of the first (& simplest) theories describing molecular geometry is VSEPR V alence S hell E lectron P air R epulsion The theory uses the concept that like charges repel to explain the geometry observed in molecules. Electron pairs (in either bonds or lone pairs) are arranged to be as far apart as possible around the atom. VSEPR (cont’d) We need to know the number of electron pairs, so if necessary draw the Lewis structure. Determine the number of: 1) 2) 3) 4)
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3 Types of Geometry Electron domain geometry is the arrangement of bonding and nonbonding electron pairs around the central atom. Molecular geometry is the arrangement of the bonded atoms around the central atom. The distinction is very important! VSEPR (cont’d) Two pair of e - : BeCl 2 VSEPR (cont’d) Double or triple bonds are considered one domain as well. HCN H-C N: This molecule is linear. The triple bond is one domain and the single bond is a second domain. What is the expected geometry of CO 2 ?
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