2 VSEPR THEORY Lewis Structures are 2D but we live in a 3D world. molecular geometry: the three-dimensional arrangement of a molecule’s atomsWhat do those 3D structure/shapes look like??Follow the Valance Shell Electron Pair Repulsion Theory or VSEPRFollowing VSEPR allows us to predict bond polarity:uneven distribution of electrons
3 Atoms bonded to central atom Number of Lone Pairs (on central) AB2 – LinearCentral atomAtoms/group of atoms attached to central atomAtoms bonded to central atomNumber of Lone Pairs (on central)Bond Angle2180˚ClBe
4 Other Linear Geometries The shape of two atoms bonded together is not given in the chart.Ex: F2What is the only possible shape a binary compound can have?LINEAR!
5 Atoms bonded to central atom AB2E1 – BentLone pairs of electrons on central atom (only)Atoms bonded to central atomNumber of Lone PairsBond Angle21<120˚What happens to the bond angle between atoms as you increase the number of “lone pair electrons” on the central atom?Bond angles decrease!
6 Atoms bonded to central atom AB2E2 – BentAtoms bonded to central atomNumber of Lone PairsBond Angle2104.5˚
7 Atoms bonded to central atom AB3 – Trigonal PlanarAtoms bonded to central atomNumber of Lone PairsBond Angle3120˚
8 AB3E1 – Trigonal Pyramidal Atoms bonded to central atomNumber of Lone PairsBond Angle31107˚
9 Atoms bonded to central atom AB4 – TetrahedralAtoms bonded to central atomNumber of Lone PairsBond Angle4109.5˚
10 Why use VSEPR Theory?Key Point: VSERP Theory is used to predict the shape of molecules based on the fact that electron pairs strongly repel each other.
11 Predicting Molecular Geometry Draw Lewis structure for molecule.Count number of lone pairs on the central atom and number of atoms bonded to the central atom.Use VSEPR to predict the geometry of the molecule.What are the molecular geometries of SO2 and SF4?SFSOAB4EAB2Etetrahedralbent