VSEPR - MOLECULAR MOLECULAR GEOMETRY GEOMETRY MOLECULAR...

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Unformatted text preview: MOLECULAR MOLECULAR GEOMETRY GEOMETRY MOLECULAR GEOMETRY 1 2 3 MOLECULAR GEOMETRY VSEPR VSEPR VSEPR VSEPR • Valence Shell Electron alence hell Pair Repulsion theory. air • Valence Shell Electron alence hell Pair Repulsion theory. air • Most important factor in determining geometry is relative repulsion between electron pairs. • Most important factor in determining geometry is relative repulsion between electron pairs. 4 No. of e- Pairs Around Central Atom 2 Example F—Be—F Geometry linear 5 No. of e- Pairs Around Central Atom 2 Example F—Be—F 180˚ F planar trigonal B F H F—Be—F F planar trigonal B 109˚ H tetrahedral 3 F F H H C H H Page 1 planar trigonal B H tetrahedral H linear F 120˚ 109˚ 4 Geometry 180˚ 120˚ 4 C 2 F F 3 120˚ H linear 6 Example 180˚ F 3 Geometry No. of e- Pairs Around Central Atom Molecule Molecule adopts the adopts the shape that shape that minimizes the minimizes the electron pair electron pair repulsions . repulsions. 109˚ 4 C H tetrahedral H H No. of e- Pairs Around Central Atom 2 7 Example F—Be—F Geometry linear 180˚ F 3 F Ammonia, NH 3 H 1. Draw electron dot structure 2. Count BP’s and LP’s = 4 3. The 4 electron pairs are at the corners corners of a tetrahedron . tetrahedron planar trigonal B F 120˚ H 109˚ 4 C H tetrahedral H Ammonia, NH 3 The electron pair geometry is tetrahedral. lone pair of electrons in tetrahedral position N H H The MOLECULAR GEOMETRY — the The MOLECULAR GEOMETRY — the The positions of the atoms — is PYRAMIDAL positions of the atoms — is PYRAMIDAL.. positions N Structure Determination Structure Determination by VSEPR by VSEPR H lone pair of electrons in tetrahedral position •• •• HNH N H H H H The ELECTRON The ELECTRON PAIR GEOMETRY is tetrahedral . tetrahedral. H H 10 11 Structure Determination Structure Determination by VSEPR by VSEPR Water, H 2O 1. Draw electron dot structure H H H H The electron pair The electron pair geometry is geometry is TETRAHEDRAL. TETRAHEDRAL. Page 2 12 Structure Determination Structure Determination by VSEPR by VSEPR Water, H 2O •• •• HOH 2. Count BP’s and LP’s = 4 3. The 4 electron pairs are at the corners of a tetrahedron. O O 9 Ammonia, NH 3 There are 4 electron pairs at the corners of a tetrahedron. •• NH lone pair of electrons in tetrahedral position H H Structure Determination Structure Determination by VSEPR by VSEPR H 8 Structure Determination Structure Determination by VSEPR by VSEPR •• •• •• •• HOH •• •• O O H H H H The molecular The molecular geometry is geometry is BENT . BENT. The electron pair The electron pair geometry is geometry is TETRAHEDRAL TETRAHEDRAL 13 Structure Determination Structure Determination by VSEPR by VSEPR Formaldehyde, CH 2O 1. Draw electron dot structure • • H O • • C O • • C H H • • • • O • • • • Methanol, CH 3OH Define bond angles 1 and 2 Angle 1 = 109 o Angle 2 = 109 o In In both cases the atom is surrounded by 4 electron pairs. electron The electron pair The electron pair geometry is PLANAR geometry is PLANAR TRIGONAL TRIGONAL C H The electron pair The electron pair geometry is PLANAR geometry is PLANAR geometry PLANAR TRIGONAL with 120o TRIGONAL with 120 o TRIGONAL with bond angles. bond angles. H The molecular The molecular geometry is also planar geometry is also planar trigonal . trigonal. 16 Structure Determination Structure Determination by VSEPR by VSEPR Acetonitrile , CH 3CN H •• H—C—O—H •• 109˚ H 109˚ 17 1 H H •• C H H C C One C is surrounded by 4 electron “lumps” and the other by 2 “lumps” C H H 2H C H O 3 C C C O H C N H 4 H Page 3 5 18 Phenylalanine Phenylalanine Phenylalanine , an amino acid Define unique bond angles H—C—C N H-C-H = 109 o 109˚ H 180˚ C-C-N C-C-N = 180 o 15 Structure Determination by VSEPR Formaldehyde, CH 2O H 2. Count BP’s and LP’s = 3 3. There are 3 electron pairs are at the corners of a planar triangle. • • 14 Structure Determination Structure Determination by VSEPR by VSEPR H 19 20 21 Central Atoms With Fewer Central Atoms With Fewer Than 4 Electron Pairs Than 4 Electron Pairs Structures with Structures with Central Atoms Central Atoms with More Than with More Than or Less Than 4 or Less Than 4 Electron Pairs Electron Pairs Boron Compounds Boron Compounds Often occurs with Group 3A elements and with those of 3rd period and higher. Consider boron trifluoride , BF3 Consider boron trifluoride , BF The 3 atom is surrounded by B only 3 electron pairs. Bond angles are 120 o •• • • •• • • F •• F • • B • • F • • •• Geometry described planar planar trigonal as as 22 Compounds with 5 or 6 Pairs Compounds with 5 or 6 Pairs Around the Central Atom Around the Central Atom 23 Compounds with 5 or 6 Pairs Compounds with 5 or 6 Pairs Around the Central Atom Around the Central Atom 90˚ F F P Trigonal bipyramid F 120˚ 5 electron pairs 24 Compounds with 5 or More Compounds with 5 or More Pairs Around the Central Atom Pairs Around the Central Atom 90˚ F F P F Trigonal bipyramid F 120˚ 5 electron pairs F F F 90˚ 6 electron pairs F F S F F F Page 4 Octahedron F 90˚ 25 26 Sulfur Tetrafluoride, SF4 Sulfur Tetrafluoride, SF4 Sulfur Tetrafluoride, SF4 Sulfur Tetrafluoride, SF4 • Number of valence electrons = • Central atom = • Dot structure Sulfur Tetrafluoride, SF4 Sulfur Tetrafluoride, SF4 • Number of valence electrons = 34 • Central atom = S • Dot structure Number of valence electrons = 34 Central atom = S •• •• •F • Dot structure •• •••• •F ••• •• •• •F ••• •• ••• S F• F ••• ••• • F• •••• • Number of valence electrons = 34 • Central atom = S • Dot structure Electron pair geometry = trigonal bipyramid (because there are 5 pairs around the S) Electron pair geometry = ? 29 Sulfur Tetrafluoride, SF4 Sulfur Tetrafluoride, SF4 Lone pair is in the equator because it requires more room. •• •• •F ••• •• ••• S F• F ••• ••• • F• •••• 90˚ S F • • F • • 90˚ S F 120˚ F F S • F• •••• 28 Sulfur Tetrafluoride, SF4 Sulfur Tetrafluoride, SF4 27 F 120˚ F F Page 5 •• •• •F • •••• S ••• •F F ••• ••• • F• •••• F• ••• ...
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This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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