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Molecular Geometry (p. 232 – 236)
Ch. 8 – Molecular Structure Molecular Geometry (p. 232 – 236)
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Teacher Notes – Why VSEPR?
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A. VSEPR Theory Valence Shell Electron Pair Repulsion Theory
Electron pairs orient themselves in order to minimize repulsive forces
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Lone pairs repel more strongly than bonding pairs!!!
A. VSEPR Theory Types of e- Pairs Bonding pairs – form bonds Lone pairs – nonbonding e- Total e- pairs– bonding + lone pairs Lone pairs repel more strongly than bonding pairs!!!
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A. VSEPR Theory Lone pairs reduce the bond angle between atoms
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B. Determining Molecular Shape
Draw the Lewis Diagram Tally up e- pairs on central atom (bonds + lone pairs) double/triple bonds = ONE pair Shape is determined by the # of bonding pairs and lone pairs Know the 13 common shapes & their bond angles!
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C. Common Molecular Shapes # 1
2 total 2 bond 0 lone → Electronic Geometry = linear Hybridization = sp BeH2 LINEAR 180°
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C. Common Molecular Shapes # 2
→ Electronic Geometry = trigonal planar Hybridization = sp2 3 total 3 bond 0 lone BF3 TRIGONAL PLANAR 120°
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C. Common Molecular Shapes # 3
3 total 2 bond 1 lone → Electronic Geometry = trigonal planar Hybridization = sp2 NO21- BENT <120°
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C. Common Molecular Shapes # 4
4 total 4 bond 0 lone → Electronic Geometry = tetrahedral Hybridization = sp3 CH4 TETRAHEDRAL 109.5°
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C. Common Molecular Shapes # 5
4 total 3 bond 1 lone → Electronic Geometry = tetrahedral Hybridization = sp3 NCl3 TRIGONAL PYRAMIDAL 107° <109.5°
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C. Common Molecular Shapes # 6
4 total 2 bond 2 lone → Electronic Geometry = tetrahedral Hybridization = sp3 H2O BENT 104.5° <109.5°
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C. Common Molecular Shapes # 7
5 total 5 bond 0 lone → Electronic Geometry = trigonal bipyramidal Hybridization = sp3d PI5 TRIGONAL BIPYRAMIDAL 120°/90°
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C. Common Molecular Shapes # 8
5 total 4 bond 1 lone → Electronic Geometry = trigonal bipyramidal Hybridization = sp3d SF4 SEESAW <120°/<90°
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C. Common Molecular Shapes # 9
→ Electronic Geometry = trigonal bipyramidal Hybridization = sp3d 5 total 3 bond 2 lone ClF3 T-SHAPE <90°
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C. Common Molecular Shapes # 10
→ Electronic Geometry = trigonal bipyramidal Hybridization = sp3d 5 total 2 bond 3 lone I31- LINEAR 180°
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C. Common Molecular Shapes # 11
6 total 6 bond 0 lone → Electronic Geometry = octahedral Hybridization = sp3d2 SH6 OCTAHEDRAL 90°
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C. Common Molecular Shapes # 12
→ Electronic Geometry = octahedral Hybridization = sp3d2 6 total 5 bond 1 lone IF5 SQUARE PYRAMIDAL <90°
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C. Common Molecular Shapes # 13
→ Electronic Geometry = octahedral Hybridization = sp3d2 6 total 4 bond 2 lone KrF4 SQUARE PLANAR 90°
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O O Se O 120° E.G. = TRIGONAL PLANAR M.G. = TRIGONAL PLANAR
D. Examples O O Se O SeO3 3 total 3 bond 0 lone E.G. = TRIGONAL PLANAR M.G. = TRIGONAL PLANAR 120° Hybridization = sp2
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M.G. = TRIGONAL PYRAMIDAL
D. Examples H As H H AsH3 4 total 3 bond 1 lone E.G. = TETRAHEDRAL M.G. = TRIGONAL PYRAMIDAL 107° (<109.5°) Hybridization = sp3
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E. Hybridization Provides information about molecular bonding and molecular shape Several atomic orbitals mix to form same total of equivalent hybrid orbitals
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E. Hybridization Carbon is common example (orbital diagram)
One of 2s electrons is promoted to 2p 4 identical orbitals form sp3 hybridization
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Remember the superscript is the orbital, not e- configuration!
E. Hybridization Other types of hybridization BeH2 forms AlCl3 forms SiF4 forms KrF4 forms SF4 forms sp sp2 sp3 d2sp3 or sp3d2 dsp3 or sp3d exceptions Remember the superscript is the orbital, not e- configuration!
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F. Hybridization Example
Compare shapes and hybrid orbitals: PF PF5 E.G. Tetrahedral Trigonal bipyramidal M.G. Trigonal pyramidal HYB sp3 dsp3
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