2 VSEPR In the valence-shell electron-pair repulsion theory (VSEPR), the electron groups around a central atom are arranged as far apart from each other as possible. have the least amount of repulsion of the negatively charged electrons. have a geometry around the central atom that determines molecular shape.
3 Guide to Predicting Molecular Shape (VSEPR Theory) 1. Write the electron-dot structure. 2. Arrange the electron groups around the central atom to minimize repulsion. 3. Use the atoms bonded to the central to determine the shape of the molecule.
8 Learning Check State the number of electron groups, lone pairs, and use VSEPR theory to determine the shape of the following molecules or ions. 1) tetrahedral 2) pyramidal3) bent A. PF 3 B. H 2 S C. CCl 4
9 Solution A. PF 3 4 electron groups, 1 lone pair, (2) pyramidal B.H 2 S 4 electron groups, 2 lone pairs, (3) bent C. CCl 4 4 electron groups, 0 lone pairs, (1) tetrahedral
10 Polar Molecules A polar molecule contains polar bonds. has a separation of positive and negative charge called a dipole indicated with + and -. has dipoles that do not cancel. + - H–Cl H — N — H dipole H dipoles do not cancel
11 Nonpolar Molecules A nonpolar molecule contains nonpolar bonds. Cl–Cl H–H or has a symmetrical arrangement of polar bonds. O=C=O Cl Cl–C–Cl Cl dipoles cancel
12 Determining Molecular Polarity STEP 1: Write the electron-dot formula. STEP 2: Determine the polarity of the bonds. STEP 3: Determine if dipoles cancel. Example: H 2 O.. H─O : H 2 O is polar │ H dipoles do not cancel
13 Learning Check Identify each of the following molecules as 1) polar or 2) nonpolar. Explain. A. PBr 3 B. HBr C. Br 2 D. SiBr 4
14 Solution Identify each of the following molecules as 1) polar or 2) nonpolar. Explain. A. PBr 3 1) pyramidal; dipoles don’t cancel; polar B. HBr1) linear; one polar bond (dipole); polar C. Br 2 2) linear; nonpolar bond; nonpolar D. SiBr 4 2) tetrahedral; dipoles cancel; nonpolar