Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals Chapter 1

Transcription

1 Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals Chapter 1 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. How to get the book of Chang? stry_10th_edition_by_raym.html istry_10th_edition_by_raym.html ١

2 Valence shell electron pair repulsion (VSEPR) model: Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. Class # of atoms bonded to # lone pairs on Arrangement of electron pairs Molecular Geometry AB linear linear B B ٢

3 0 lone pairs on Cl Be Cl 2 atoms bonded to Class AB linear linear 2 # of atoms bonded to # lone pairs on AB VSEPR Arrangement of electron pairs planar Molecular Geometry planar ٣

4 Class AB linear linear 2 # of atoms bonded to # lone pairs on AB VSEPR Arrangement of electron pairs planar Molecular Geometry planar AB tetrahedral tetrahedral ٤

5 Class # of atoms bonded to VSEPR # lone pairs on Arrangement of electron pairs Molecular Geometry AB linear linear 2 AB planar planar AB tetrahedral tetrahedral AB ٥

6 Class # of atoms bonded to VSEPR # lone pairs on Arrangement of electron pairs Molecular Geometry AB linear linear 2 AB planar planar AB tetrahedral tetrahedral AB AB octahedral octahedral ٦

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8 lone-pair vs. lone pair repulsion lone-pair vs. bonding > > pair repulsion bonding-pair vs. bonding pair repulsion VSEPR Class # of atoms bonded to # lone pairs on AB AB 2 E 2 1 Arrangement of electron pairs planar planar Molecular Geometry planar bent ٨

9 VSEPR Class # of atoms bonded to # lone pairs on Arrangement of electron pairs Molecular Geometry AB tetrahedral tetrahedral AB 3 E 3 1 tetrahedral pyramidal VSEPR Class # of atoms bonded to # lone pairs on Arrangement of electron pairs Molecular Geometry AB tetrahedralt tetrahedralt AB 3 E 3 1 tetrahedral pyramidal AB 2 E tetrahedral bent O H H ٩

10 Class # of atoms bonded to VSEPR # lone pairs on AB AB 4 E 4 1 Arrangement of electron pairs Molecular Geometry distorted tetrahedron (see-saw) Class # of atoms bonded to VSEPR # lone pairs on AB AB 4 E 4 1 AB 3 E Arrangement of electron pairs Molecular Geometry distorted tetrahedron T-shaped F F Cl F ١٠

11 Class # of atoms bonded to VSEPR # lone pairs on AB AB 4 E 4 1 AB 3 E AB 2 E Arrangement of electron pairs Molecular Geometry distorted tetrahedron T-shaped linear I I I VSEPR Class # of atoms bonded to # lone pairs on Arrangement of electron pairs Molecular Geometry AB octahedral octahedral AB 5 E 5 1 octahedral square pyramidal F F F Br F F ١١

12 VSEPR Class # of atoms bonded to # lone pairs on Arrangement of electron pairs Molecular Geometry AB octahedral octahedral AB 5 E 5 1 octahedral AB 4 E octahedral square pyramidal square planar F F Xe F F ١٢

13 Predicting Molecular Geometry 1. Draw Lewis structure for molecule. 2. Count number of lone pairs on the and number of atoms bonded to the. 3. Use VSEPR to predict the geometry of the molecule. What are the molecular geometries of SO 2 and SF 4? O S O F AB 4 E 4 AB 2 E bent F S F F distorted Tetrahedron (see-saw) Dipole Moments and Polar Molecules electron poor region H electron rich region F δ+ δ µ = Q x r Q is the charge r is the distance between charges 1 D = 3.36 x C m 10.2 ١٣

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15 Which of the following molecules have a dipole moment? H 2 O, CO 2, SO 2, and CH 4 O dipole moment polar molecule S dipole moment polar molecule O C O no dipole moment nonpolar molecule H H C H H no dipole moment nonpolar molecule 10.2 Does BF 3 have a dipole moment? 10.2 ١٥

16 Does CH 2 Cl 2 have a dipole moment? ١٦

17 Chemistry In Action: Microwave Ovens How does Lewis theory explain the bonds in H 2 and F 2? Sharing of two electrons between the two atoms. Bond Dissociation Energy Bond Length Overlap Of H kj/mole 74 pm 2 1s F kj/mole 142 pm 2 2p Valence bond theory bonds are formed by sharing of e - from overlapping atomic orbitals ١٧

18 Change in Potential Energy of Two Hydrogen Atoms as a Function of Their Distance of Separation 10.3 Change in electron density as two hydrogen atoms approach each other ١٨

19 N 1s 2 2s 2 2p 3 3 H 1s 1 Valence Bond Theory and NH 3 If the bonds form from overlap of 3 2p orbitals on nitrogen with the 1s orbital on each hydrogen atom, what would the molecular geometry of NH 3 be? If use the 3 2p orbitals predict 90 0 Actual H-N-H bond angle is 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 10.4 ١٩

20 Formation of sp 3 Hybrid Orbitals ٢٠

21 Predict correct bond angle 10.4 Formation of sp Hybrid Orbitals 10.4 ٢١

22 Formation of sp 2 Hybrid Orbitals 10.4 How do I predict the hybridization of the? 1. Draw the Lewis structure of the molecule. 2. Count the number of lone pairs AND the number of atoms bonded to the # of Lone Pairs + # of Bonded Atoms Hybridization Examples 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 ٢٢

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24 10.5 Sigma bond (σ) electron density between the 2 atoms Pi bond (π) electron density above and below plane of nuclei of the bonding atoms 10.5 ٢٤

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26 10.5 Describe the bonding in CH 2 O. H H C O C 3 bonded atoms, 0 lone pairs C sp ٢٦

27 Sigma (σ) and Pi Bonds (π) Single bond 1 sigma bond Double bond 1sigma bond and 1 pi bond Triple bond 1 sigma bond and 2 pi bonds How many σ and π bonds are in the acetic acid (vinegar) molecule CH 3 COOH? H O H C C O H σ bonds = = 7 π bonds = 1 H 10.5 END OF CHAPTER1 ٢٧