simmerling_Lect-29

simmerling_Lect-29 - Lec-29: Molecular Geometry - VSEPR Roy...

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Roy A. Lacey, Stony Brook University; Che 131, Fall 2011 1 Lec-29: Molecular Geometry - VSEPR Molecular shape affects the properties of compounds: Physical state at any temp solubility in fluids chemical reactivity biological activity distribution in the environment Roy A. Lacey, Stony Brook University; Che 131, Fall 2011 2 Molecular Shape Being able to understand and predict coordination geometry is very important
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Most drugs act by interacting with a specific chiral biological “receptor” molecule Shape determines which directions the functional groups are pointing (and thus the binding strength)
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forward back Roy A. Lacey, Stony Brook University; Che 131, Fall 2011 7 Lewis structures do not provide enough Information to establish the shapes of molecules A bond angle is the angle defined by lines joining the centers of two atoms to a third atom to which they are covalently bonded. The molecular geometry or shape is defined by the lowest energy arrangement of its atoms in three- dimensional space. Why do water and CO 2 have different molecular geometries?
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Electron pair geometry Relative positions in space of all bonding pairs and lone pairs around the central atom Molecular geometry Relative positions in space of all of the atoms We need the eletron pair geometry in order to calculate the molecular geometry. Roy A. Lacey, Stony Brook University; Che 131, Fall 2011 9 Valence-Shell Electron-Pair Repulsion Theory (VSEPR) The geometric arrangement of atoms bonded to a given atom is determined principally by minimizing electron pair repulsions. AX 2
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10 Valence-Shell Electron-Pair Repulsion Theory (VSEPR) (1)Electron pairs repel each other and try to remain as far apart from one another as possible. (2)The positions of atoms in space (molecular geometry or configuration about a central atom) is determined by the relative positions that electron pairs achieve after taking repulsions into account.
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simmerling_Lect-29 - Lec-29: Molecular Geometry - VSEPR Roy...

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