BLB9S - Chemistry 101 Prof. Jerry Keister Chapter 7 1...

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Chapter 7 1 Chemistry 101 Chemistry 101 Prof. Jerry Keister
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Chapter 7 2 Molecular Geometry and Molecular Geometry and Bonding Theory Bonding Theory Chapter 9 Chapter 9
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Chapter 7 3 Molecular Shapes Molecular Shapes Lewis structures give atomic connectivity: they tell us which atoms are physically connected to which. The shape of a molecule is determined by its bond angles. Consider CCl 4 : experimentally we find all Cl-C-Cl bond angles are 109.5 ° . Therefore, the molecule cannot be planar. All Cl atoms are located at the vertices of a tetrahedron with the C at its center.
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Chapter 7 4 Molecular Shapes Molecular Shapes
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Chapter 7 5 Molecular Shapes Molecular Shapes In order to predict molecular shape, we assume the valence electrons repel each other. Therefore, the molecule adopts the 3D geometry which minimizes these repulsions. We call this the V alence S hell E lectron P air R epulsion ( VSEPR ) theory.
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Chapter 7 6 The VSEPR Model The VSEPR Model The valence electrons in a molecule are the bonding pairs of electrons as well as the lone pairs. There are 11 shapes that are important to us: linear (3 atoms, AB 2 ); bent (3 atoms, AB 2 ); trigonal planar (4 atoms, AB 3 ); trigonal pyramidal (4 atoms, AB 3 ); T-shaped (4 atoms, AB 3 ); tetrahedral (5 atoms, AB 4 ); square planar (5 atoms, AB 4 ); see- saw (5 atoms, AB 4 ); trigonal bipyramidal (6 atoms, AB 5 ); square pyramidal (6 atoms, AB 5 ); and octahedral (7 atoms, AB 6 ).
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Chapter 7 7 The VSEPR Model The VSEPR Model
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Chapter 7 8 The VSEPR Model The VSEPR Model Predicting Molecular Geometries Predicting Molecular Geometries To determine the shape of a molecule, we distinguish between lone pairs (or non-bonding pairs, those not in a bond) of electrons and bonding pairs (those found between two atoms). We define the electron pair geometry by the positions in 3D space of ALL electron pairs (bonding or non- bonding). The electrons adopt an arrangement in space to minimize e - -e - repulsion.
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Chapter 7 9 The VSEPR Model The VSEPR Model Predicting Molecular Geometries Predicting Molecular Geometries
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Chapter 7 10 The VSEPR Model The VSEPR Model Predicting Molecular Geometries Predicting Molecular Geometries
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Chapter 7 11 The VSEPR Model The VSEPR Model We determine the electron pair geometry only looking at electron pairs, bonding and non-bonding (lone pairs). We name the molecular geometry by the positions of atoms. We ignore lone pairs in the molecular geometry.
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Chapter 7 12 Predicting Molecular Geometries Predicting Molecular Geometries To determine the molecular geometry: draw the Lewis structure count the total number of electron pairs around the central atom arrange the electron pairs in one of the above geometries to minimize e - -e - repulsion (multiple bonds count as one bonding pair) look at the atomic positions to describe molecular geometry
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Chapter 7 13 The VSEPR Model The VSEPR Model Predicting Molecular Geometries Predicting Molecular Geometries
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Chapter 7 14 The VSEPR Model The VSEPR Model Predicting Molecular Geometries Predicting Molecular Geometries
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BLB9S - Chemistry 101 Prof. Jerry Keister Chapter 7 1...

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