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Ch 6.5 Molecular Geometry. VSEPR Theory  Use VSEPR theory Valence-Shell-Electron-Pair Repulsion =the repulsion between electron pairs causes molecular.

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Presentation on theme: "Ch 6.5 Molecular Geometry. VSEPR Theory  Use VSEPR theory Valence-Shell-Electron-Pair Repulsion =the repulsion between electron pairs causes molecular."— Presentation transcript:

1 Ch 6.5 Molecular Geometry

2 VSEPR Theory  Use VSEPR theory Valence-Shell-Electron-Pair Repulsion =the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.  Determined by number of valence electrons of the central atom  3-D shape is a result of bonded pairs and lone pairs of electrons

3 Bonding and Shape of Molecules Number of Bonds Number of Unshared Pairs ShapeExamples Linear Trigonal planar Tetrahedral Pyramidal Bent or Angular BeCl 2 BF 3 CH 4, SiCl 4 NH 3, PCl 3 ONF AB 2 Covalent Structure AB 3 AB 4 AB 3 E AB 2 E

4 Number of Bonds Number of Unshared Pairs Covalent Structure ShapeExample 22AB 2 E 2 Bent or Angular H2OH2O 5 0AB 5 Trigonal Bipyramidal PF 5 60AB 6 OctahedralSF 6

5 .. The VSEPR Model OO C Linear OO S Bent OO S O Trigonal planar F F F N Trigonal pyramidal F F F P F F Trigonal bipyramidal Octahedral F F F S F F F AB 6 SO 2 F F F C F Tetrahedral

6 Methane CH 4 CH H H H C o H H H H Tetrahedral geometry

7 Ammonia- NH 3 N HH H N 107 o H H H.. H H H N Trigonal Pyramidal geometry N HH H

8 O.. Water –H 2 O.. HH O Bent geometry SO 2 HH..

9 B F F F Boron trifluoride - BF 3 B F F F 120 o Trigonal planar

10 Carbon dioxide – CO 2 OO C Linear CO O

11 C o H H H H N 107 o H H H.. O o H H.. Tetrahedral Pyramidal Bent

12 Learning Check Determine the molecular geometry: A. CCl 4 B. H 2 CO

13 Learning Check Determine the molecular geometry: A. CCl 4 Tetrahedral B. H 2 CO

14 Learning Check Determine the molecular geometry: A. CCl 4 Tetrahedral B. H 2 CO Trigonal Planar

15 Intermolecular Forces  Forces of attraction between molecules  Very weak compared to ionic and metallic bonding.  The strongest occur between polar molecules.

16 Intermolecular Forces  Dipole: One end slightly positive and one end slightly negative.  Can show the polar nature with an arrow pointing to the more electronegative atom. O H HH Cl

17  Just because a molecule has a polar bond does not make it a polar molecule.  The bond polarities cancel if they are in opposite directions.  Example: CO 2

18 Attractions Between Molecules  The two weakest attractions between molecules.  Dipole Interactions When polar molecules are attracted to one another.  Dispersions Forces Caused by the motion of electrons Weakest of all interactions.

19 Hydrogen Bonds  A strong attraction found in hydrogen- containing molecules.  A hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom. Example  Water

20 Homework  6.5 page 210 #33-34, NOT 37-42!!


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