Ch 9 VSEPR and valence bond theory.pdf

Tetrahedral electron domain geometry with three

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Tetrahedral electron domain geometry with three bonded atoms and one lone pair, showing only the atoms S. Ensign, Chem. 1210 30 Trigonal pyramidal molecular geometry (shape)
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Tetrahedral electron pair geometry with two bonded atoms and two lone pairs (AX 2 E 2 ) S. Ensign, Chem. 1210 31 Bent molecular geometry (shape)
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Tetrahedral electron pair geometry with two bonded atoms and two lone pairs , showing only the atoms S. Ensign, Chem. 1210 32 Bent molecular geometry (shape)
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Molecular geometries of molecules with tetrahedral e - domain geometries Trigonal pyramidal Tetrahedral Bent S. Ensign, Chem. 1210 33
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Electron pair (domain) geometry: the arrangement of electron pairs in space about a central atom Molecular geometry: the arrangement of bonded atoms in space about a central atom when a central atom has no lone pairs (no nonbonded e - pairs), then the e - domain domain geometry = the molecular geometry • when a central atom has one or more lone when a central atom has one or more lone pairs, these lone pairs will influence the molecular geometry (shape of the molecule) S. Ensign, Chem. 1210 34 molecular geometry (shape of the molecule) due to VSEPR
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Predicting molecular geometry (1) D d L i t t (1) Draw a good Lewis structure (2) Count the number of electron pairs around the central atom Double and triple bonds count as one central atom. Double and triple bonds count as one e- pair (3) Determine # of bonding electron pairs and number (3) Determine # of bonding electron pairs and number of nonbonding electron pairs (nonbonding pairs occupy positions that best minimize electron pair occupy positions that best minimize electron pair repulsion) (4) Molecular shape is described in terms of the arrangement of the bonding pairs of electrons Example: Compare the e- pair geometries and S. Ensign, Chem. 1210 35 Example: Compare the e pair geometries and molecular shapes of H 2 O, NH 3 , and CH 4
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Compare the e- pair geometries and molecular shapes of H 2 O, NH 3 , and CH 4 (1) Draw a good Lewis structure (2) Count the number of electron pairs around the t l t D bl d central atom. Double and triple bonds count as one e- pair (3) Determine # of bonding (3) Determine # of bonding electron pairs and number of nonbonding electron pairs (nonbonding pairs occupy positions that best minimize electron pair repulsion) (4) Molecular shape is described in terms of the described in terms of the arrangement of the bonding pairs of electrons S. Ensign, Chem. 1210 36
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Different representations of ammonia and water NH 3 Formula Lewis Structure Electron domain geometry Molecular geometry H 2 O Formula Lewis Electron domain Molecular S. Ensign, Chem. 1210 37 Structure geometry Molecular geometry
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