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:
Ch 6.5 Molecular Geometry
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
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
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
.. 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
Methane CH 4 CH H H H C o H H H H Tetrahedral geometry
Ammonia- NH 3 N HH H N 107 o H H H.. H H H N Trigonal Pyramidal geometry N HH H
O.. Water –H 2 O.. HH O Bent geometry SO 2 HH..
B F F F Boron trifluoride - BF 3 B F F F 120 o Trigonal planar
Carbon dioxide – CO 2 OO C Linear CO O
C o H H H H N 107 o H H H.. O o H H.. Tetrahedral Pyramidal Bent
Learning Check Determine the molecular geometry: A. CCl 4 B. H 2 CO
Learning Check Determine the molecular geometry: A. CCl 4 Tetrahedral B. H 2 CO
Learning Check Determine the molecular geometry: A. CCl 4 Tetrahedral B. H 2 CO Trigonal Planar
Intermolecular Forces Forces of attraction between molecules Very weak compared to ionic and metallic bonding. The strongest occur between polar molecules.
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
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
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.
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