Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals

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1 Chemical Bonding II: and ybridization of Atomic rbitals Chapter 10 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 linear linear B B Cl Be Cl 2 0 atoms lone bonded pairs to central atom 1

2 VSEPR AB linear linear AB VSEPR Trigonal Planar arrangement VSEPR AB AB 2 E 2 1 bent AB linear linear AB AB tetrahedral tetrahedral 2

3 VSEPR Tetrahedral Arrangement AB tetrahedral tetrahedral AB 3 E 3 1 tetrahedral pyramidal VSEPR Tetrahedral Arrangement AB tetrahedral tetrahedral AB 3 E 3 1 tetrahedral pyramidal AB 2 E tetrahedral bent AB linear linear AB VSEPR AB tetrahedral tetrahedral AB

4 VSEPR Trigonal Bipyramid Arrangement AB AB 4 E 4 1 See-Saw (distorted tetrahedron) VSEPR Trigonal Bipyramid Arrangement VSEPR Trigonal Bipyramid Arrangement AB AB 4 E 4 1 AB 3 E See-Saw T-shaped Cl AB AB 4 E 4 1 AB 3 E AB 2 E See-Saw T-shaped linear I I I 4

5 VSEPR AB linear linear AB AB tetrahedral tetrahedral AB AB octahedral octahedral VSEPR ctahedral Arrangement VSEPR ctahedral Arrangement AB octahedral octahedral AB 5 E 5 1 octahedral square pyramidal Br AB octahedral octahedral AB 5 E 5 1 octahedral AB 4 E octahedral square pyramidal square Xe 5

6 lone-pair vs. lone pair repulsion lone-pair vs. bonding > > pair repulsion bonding-pair vs. bonding pair repulsion 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. AB 2 E What are the molecular geometries of S 2 and S 4? (In S 4, S uses an expanded octet of 10.) S bent S S AB 4 E See-Saw (distorted Tetrahedron) 6

7 Dipole Moments and Polar Molecules electron poor region electron rich region Which of the following molecules have a dipole moment? 2, C 2, S 2, and C 4 Chemistry In Action: Microwave vens dipole moment polar molecule S dipole moment polar molecule C C no dipole moment nonpolar molecule no dipole moment nonpolar molecule

8 2 2 ow does Lewis theory explain the bonds in 2 and 2? Sharing of two electrons between the two atoms. Bond Dissociation Energy kj/mole kj/mole Bond Length 74 pm 142 pm verlap f 2 1s 2 2p Valence bond theory bonds are formed by sharing of e - from overlapping atomic orbitals ybridization 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). ybrid 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. verlap of hybrid orbitals with atomic orbitals b. verlap of hybrid orbitals with other hybrid orbitals 10.4 ormation of sp 2 ybrid rbitals

9 ormation of sp ybrid rbitals ow do I predict the hybridization of the? Count the number of lone pairs AND the number of atoms the # of Lone Pairs + # of Bonded Atoms ybridization Examples 2 sp BeCl 2 3 sp 2 B 3 4 sp 3 C 4, N 3, 2 5 sp 3 d PCl sp 3 d 2 S Sigma ( ) and Pi Bonds ( ) Single bond Double bond Triple bond 1 sigma bond 1 sigma bond and 1 pi bond 1 sigma bond and 2 pi bonds ow many and bonds are in the acetic acid (vinegar) molecule C 3 C? C C bonds = = 7 bonds =

10 Pi bond ( ) electron density above and below plane of nuclei Sigma bond ( ) electron density between the 2 atoms of the bonding atoms No unpaired e - Should be diamagnetic Experiments show 2 is paramagnetic (has UNPAIRED e-) M Theory is NT in the AP Chemistry Curriculum and will NT be on the AP exam! This is just a quick overview! orbital theory bonds are formed from interaction of atomic orbitals to form molecular orbitals

11 Energy levels of bonding and antibonding molecular orbitals in hydrogen ( 2 ). A bonding molecular orbital has lower energy and greater stability than the atomic orbitals from which it was formed. An antibonding molecular orbital has higher energy and lower stability than the atomic orbitals from which it was formed rbital (M) Configurations 1. The number of molecular orbitals (Ms) formed is always equal to the number of atomic orbitals combined. 2. The more stable the bonding M, the less stable the corresponding antibonding M. 3. The filling of Ms proceeds from low to high energies. 4. Each M can accommodate up to two electrons. 5. Use und s rule when adding electrons to Ms of the same energy. 6. The number of electrons in the Ms is equal to the sum of all the electrons on the bonding atoms

12 bond order = 1 2 ( - ) Number of electrons in bonding Ms Number of electrons in antibonding Ms Delocalized molecular orbitals are not confined between two adjacent bonding atoms, but actually extend over three or more atoms. bond order ½ 1 ½