Electron Count stable noble gas electron configurations Octet rule for most elements 2 for H 6 for group 3A B and Al 10 or 12 for 3rd shell P and S ConcepTest How many unused electrons on the central atom single bonds double bonds and triple bonds respectively appear in the Lewis structure of PF 6 A 0 3 3 0 B 0 6 0 0 C 1 3 3 0 D 1 6 0 0 E 2 6 0 0 F none of these ConcepTest What is the geometry for AlCl3 A octahedral B trigonal bipyramidal D trigonal planar E linear C tetrahedral VSEPR Valence Shell Electron Pair Repulsion Pairs of electrons occupy space Pairs Bonding and nonbonding Sharing electrons Lewis structure VSEPR Linear 180 2 pairs Trigonal planar 120 3 pairs Tetrahedral 109 4 pairs Trigonal bipyramidal 120 90 5 pairs Octahedral 60 ex PF6 6 pairs ConcepTest What are the electron pair and molecular geometries for PCl 3 A octahedron trigonal bipyramid B trigonal bipyramid tetrahedron C tetrahedron trigonal pyramid D trigonal pyramid bent VSEPR Single Bonds and Lone Pairs Electron pair geometry pairs around central atom Molecular geometry atoms only E none of these Tetrahedral Methane CH4 4 bond pairs no lone pairs 109 5 Trigonal pyramidal 107 5 Ammonia NH3 3 bond pairs 1 lone pair Bent 104 5 Water H2O 2 bond pairs 2 lone pairs All same shape but methane has all four bond pairs while ammonia has only 3 and water has only 2 VSEPR Five Six Pairs Electron pair geometry Trigonal Bipyramidal Trigonal Bipyramidal PF5 5 bond pairs no lone pairs Seesaw SF4 4 bond pairs 1 lone pair T Shaped ClF3 4 bond pairs 2 lone pairs Linear XeF2 2 bond pairs 3 lone pairs Electron pair geometry Octahedral Octahedral SF6 6 bond pairs no lone pairs Square Pyramid BaF5 5 bond pairs 1 lone pair Square planar XeF4 4 bond pairs 2 lone pairs Previous Chapter Electrons in atom valence electron This Chapter share electrons between atoms making molecules simplest model Lewis shapes geometries bonds molecular properties A B How are they sharing Atoms share them equally Ex H H influence on electrons between two hydrogens will be the same Not true if we have different atoms Ex H F don t share electrons equally Charge distribution making charge If electrons go towards F F will have a partial negative while hydrogen has a partial positive Measure of sharing Electronegativity increases up and to the right on periodic table ConcepTest Which pair has the higher electronegativity listed FIRST A B C B C N C N O D O F E Cl F F Cl S Covalent Polar Covalent Ionic Continuous ENA B 0 5 0 7 1 8 2 0