Topic: Molecular Shape Do Now: Draw Lewis Dot Diagram for the following two compounds 1. CH 2 F 2 2. CaO [ Ca ] +2

Use the Lewis Structure Lewis structure is 2-D, but can help figure out 3-D shape H O H

REMINDER:Bonding Capacity 00:Ne: Ne, Ar, Kr 22·O: O, S 33·N· N, P 44·C· C, Si 11·F: F, Cl, Br, I 11HH Bonding Capacity # Unpaired Electrons Lewis Structure Atom · ··

Molecular Shape Determined by overlap of orbitals Shape determined by two factors: 1. # e - groups (pairs) around the central atom – pay close attention to the “free electron pairs” 2. total # atoms bonded to central atom Free electron pairs Central Atom

VSEPR (A model used to predict the shape of individual molecules based on the extent of electron-pair electrostatic repulsion) VSEPR= Valence shell electron pair repulsion: –Basically free electrons will repel one another causing the molecule to bend

2 atoms (no central atom) Always linear –Examples H 2 O 2 N 2 HCl

3 atoms Can be linear or bent –Must look at central atom If free electrons, then will be bent Central atom No free electrons so linear Central atom Free electrons so bent

4 atoms that form triangles Look at central atom –No free electrons = trigonal planar - Free electrons = trigonal pyramidal

4-Atom Molecules: Planar = no real central atom, no free electrons either

5 atom molecules Always tetrahedral –Examples CCl 4 CH 4 CH 2 I 2

Summary of Molecular Shapes Start with Lewis Structure! Look at total number of atoms Look at # of atoms bonded to central atom Look at free pair(s) of electrons around central atom

  SymmetricalMolecules  Nonpolar Nonpolar

Asymmetric Molecules  Polar  Bent & trigonal pyramidal are always polar

Let’s try a few… Name the SHAPE and POLARITY

BENT POLAR

Trigonal Planar POLAR

Tetrahedral POLAR

Trigonal Pyramidal POLAR

linear POLAR

linear POLAR

bent POLAR

tetrahedral NONPOLAR