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Chapter 9 Molecular Geometry and Bonding Theories.

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Presentation on theme: "Chapter 9 Molecular Geometry and Bonding Theories."— Presentation transcript:

1 Chapter 9 Molecular Geometry and Bonding Theories

2 Trigonal Bipyramidal Electron Domain –Trigonal bipyramidal –Seesaw –T-shaped –Linear Table 9.3

3 Shapes of Larger Molecules Consider the geometry about a particular atom rather than the geometry of the molecule as a whole

4 Larger molecules tend to react at a particular site in the molecule Called a functional group Shapes of Larger Molecules acetic acid

5 Molecular Shape and Molecular Polarity A molecule possessing polar bonds does not imply that the molecule as a whole will be polar Fig 9.11 CO 2, a nonpolar molecule

6 To determine the overall dipole moment for the molecule, add the individual bond dipoles vectorially Molecular Shape and Molecular Polarity Fig 9.12

7 Molecular Shape and Molecular Polarity Fig 9.13 Molecules containing polar bonds Polar Nonpolar Polar

8 Valence bond theory – bonds are formed by sharing of e − from overlapping atomic orbitals (AOs) Overlap of:2 1s orbitals How does Lewis theory explain the bonds in H 2 and HCl? “Sharing of two electrons between the two atoms ” Covalent Bonding and Orbital Overlap 1s orbital and 3p orbital

9 Fig 9.15 Formation of the H 2 molecule 74 pm

10 Hybrid Orbitals VSEPR theory allows prediction of molecular shapes How can tetrahedral, trigonal bipyramidal, and other geometries arising from the atomic orbitals we recognize?

11 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 = 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 sp Hybrid Orbitals F F Be VSEPR predicts: Linear, 180° Be Assume Be absorbs the small amount of energy needed to promote an electron from the 2s to the 2p orbital: it can form two bonds.

13 sp Hybrid Orbitals F F Be VSEPR predicts: Linear, 180° Mixing the s and p orbitals yields two degenerate orbitals that are hybrids of the two orbitals: –These sp hybrid orbitals have two lobes like a p orbital. –One of the lobes is larger and more rounded as is the s orbital. Fig 9.16 formation of sp hybrid orbitals

14 These two degenerate orbitals would align themselves 180  from each other This is consistent with the observed geometry of beryllium compounds: linear sp Hybrid Orbitals Fig 9.17 Formation of two equivalent Be-F bonds in BeF 2

15 Using a similar model for boron leads to… sp 2 Hybrid Orbitals Fig 9.18

16 With carbon we get… sp 3 Hybrid Orbitals Fig 9.19

17 For geometries involving expanded octets on the central atom, we must use d orbitals in our hybrids : Hybridization Involving d Orbitals

18 This leads to five degenerate sp 3 d orbitals… …or six degenerate sp 3 d 2 orbitals. Hybridization Involving d Orbitals

19 # of Lone Pairs + # of Bonded Atoms HybridizationExamples 2 3 4 5 6 sp sp 2 sp 3 sp 3 d sp 3 d 2 BeCl 2 BF 3 CH 4, NH 3, H 2 O PCl 5 SF 6 How do I predict the hybridization of the central atom? Count the number of lone pairs AND the number of atoms bonded to the central atom

20 Sigma () Bonds  Characterized by:  Head-to-head overlap  Single bonds are always  bonds Fig 9.14

21 Pi () Bonds  Pi bonds are characterized by:  Side-to-side overlap In a multiple bond: one of the bonds is a  bond and the rest are  bonds Fig 9.22

22 Multiple bonds in ethylene Fig 9.23 Molecular geometry of ethylene Fig 9.24 The σ bonds in ethylene sp 2

23 Multiple Bonds

24 The π bond in ethylene Fig 9.25


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