CHAPTER TEN MOLECULAR GEOMETRY MOLECULAR GEOMETRY V S E P R CHEMICAL BONDING II: MOLECULAR GEOMETRY AND HYBRIDIZATION OF ATOMIC ORBITALS

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1 CHAPTER TEN CHEMICAL BONDING II: AND HYBRIDIZATION O ATOMIC ORBITALS V S E P R VSEPR Theory In VSEPR theory, multiple bonds behave like a single electron pair Valence shell electron pair repulsion (VSEPR) model: Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. AB B B 1

2 Cl Be Cl AB linear linear AB

3 AB linear linear AB AB planar planar AB linear linear AB planar planar AB tetrahedral tetrahedral AB

4 AB linear linear AB planar planar AB tetrahedral tetrahedral AB AB

5 AB AB 2 E 2 1 planar planar planar 5

6 AB tetrahedral tetrahedral AB 3 E 3 1 tetrahedral AB tetrahedral tetrahedral AB 3 E 3 1 tetrahedral pyramidal AB 2 E tetrahedral H O H AB AB 4 E 4 1 6

7 AB AB 4 E 4 1 AB 3 E distorted tetrahedron Cl AB AB 4 E 4 1 AB 3 E AB 2 E I I I distorted tetrahedron T-shaped AB octahedral octahedral AB 5 E 5 1 octahedral Br 7

8 AB octahedral octahedral AB 5 E 5 1 octahedral AB 4 E octahedral square pyramidal Xe 10.1 Predicting 1. Draw Lewis structure for molecule. 2. Count number of lone the and number of atoms the. 3. Use VSEPR to predict the geometry of the molecule. What are the molecular geometries of SO 2 and S 4? 8

9 DIPOLE MOMENTS Bonds and molecules may be polar or nonpolar Relative to distribution of electrons Dipole moment (µ= Q x r) Bonds Molecule DIPOLE MOMENTS Dipole Moments and Polar Molecules electron poor region H electron rich region δ+ δ- DIPOLE MOMENTS H 2 O vs CO 2 B 3 vs NH 3 cis-c 2 H 2 Cl 2 vs trans- C 2 H 2 Cl 2 9

10 DIPOLE MOMENTS H 2 O vs CO 2 B 3 vs NH 3 cis-c 2 H 2 Cl 2 vs trans- C 2 H 2 Cl 2 NH 3 vs N

11 DIPOLE MOMENTS Does CH 2 Cl 2 have a dipole moment? VALENCE BOND THEORY Change in electron density as two hydrogen atoms approach each other. 11

12 VALENCE BOND THEORY Covalent bond consists of pair of electrons of opposite spin within an AO Appears that to form bond, must have unpaired electron New AO--hybrid orbital Mix AO before bonding occurs Explains # of bonds and bond angles VALENCE BOND THEORY Hybridization mixing of two or more atomic orbitals to form a new set of hybrid orbitals. 1. Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybrid orbitals have very different shape from original atomic orbitals. 2. Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process. 3. Covalent bonds are formed by: a. Overlap of hybrid orbitals with atomic orbitals b. Overlap of hybrid orbitals with other hybrid orbitals 12

13 VALENCE BOND THEORY Draw Lewis Structure Count valence (multiples = 1) # valence pairs = # hybrid orbitals (Table 10.4) VALENCE BOND THEORY Ground state orbital diagram (valence) Excitation Hybridization CH 4, 13

14 What about NH 3? 14

15 VALENCE BOND THEORY Ground state orbital diagram (valence) Excitation Hybridization B 3, ormation of sp 2 Hybrid Orbitals VALENCE BOND THEORY Ground state orbital diagram (valence) Excitation Hybridization BeCl 2, 15

16 ormation of sp Hybrid Orbitals VALENCE BOND THEORY Ground state orbital diagram (valence) Excitation Hybridization S 6, HYBRIDIZATION O MULTIPLE BONDS Extra electrons not located in hybrid orbitals Sigma Bond Pi Bond 16

17 C 2 H 4 (Lewis Structure) Each C is HYBRIDIZATION O MULTIPLE BONDS C 2 H 4 (Lewis Structure) Each C is HYBRIDIZATION O MULTIPLE BONDS 17

18 C 2 H 2 (Lewis Structure) Each C is HYBRIDIZATION O MULTIPLE BONDS HYBRIDIZATION O MULTIPLE BONDS 18

19 HYBRIDIZATION O MULTIPLE BONDS Sigma (σ) and Pi Bonds (π) Single bond Double bond Triple bond How many σ and π bonds are in the acetic acid (vinegar) molecule CH 3 COOH? σ bonds = π bonds = 19