1 Cl Be Cl MOLECULAR GEOMETRY # of atoms # lone bonded to - PDF document

CHAPTER TEN CHEMICAL BONDING II: MOLECULAR GEOMETRY AND HYBRIDIZATION OF ATOMIC ORBITALS MOLECULAR GEOMETRY V S E P R VSEPR Theory  In VSEPR theory, multiple bonds behave like a single electron pair MOLECULAR GEOMETRY Valence shell electron pair repulsion (VSEPR) model: Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB 2 2 0 B B 1

Cl Be Cl MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular central atom central atom electron pairs Class Geometry AB 2 2 0 linear linear AB 3 3 0 2

MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB 2 2 0 linear linear trigonal trigonal AB 3 3 0 planar planar AB 4 4 0 MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB 2 2 0 linear linear trigonal trigonal AB 3 3 0 planar planar AB 4 4 0 tetrahedral tetrahedral AB 5 5 0 3

MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular central atom central atom electron pairs Class Geometry AB 2 2 0 linear linear trigonal trigonal AB 3 3 0 planar planar AB 4 4 0 tetrahedral tetrahedral trigonal trigonal AB 5 5 0 bipyramidal bipyramidal AB 6 6 0 4

MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry trigonal trigonal AB 3 3 0 planar planar trigonal AB 2 E 2 1 planar 5

MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry tetrahedral tetrahedral AB 4 4 0 tetrahedral AB 3 E 3 1 MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular central atom central atom electron pairs Class Geometry AB 4 4 0 tetrahedral tetrahedral trigonal AB 3 E 3 1 tetrahedral pyramidal AB 2 E 2 2 2 tetrahedral O H H MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular central atom central atom electron pairs Class Geometry trigonal trigonal AB 5 5 0 bipyramidal bipyramidal trigonal AB 4 E 4 1 bipyramidal 6

MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry trigonal trigonal AB 5 5 0 bipyramidal bipyramidal trigonal distorted AB 4 E 4 1 bipyramidal tetrahedron trigonal AB 3 E 2 3 2 bipyramidal F F Cl F MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry trigonal trigonal AB 5 5 0 bipyramidal bipyramidal trigonal distorted AB 4 E 4 1 bipyramidal tetrahedron trigonal T-shaped AB 3 E 2 3 2 bipyramidal I trigonal AB 2 E 3 2 3 bipyramidal I I MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB 6 6 0 octahedral octahedral AB 5 E 5 1 octahedral F F F Br F F 7

MOLECULAR GEOMETRY # of atoms # lone bonded to pairs on Arrangement of Molecular Class central atom central atom electron pairs Geometry AB 6 6 0 octahedral octahedral square octahedral AB 5 E 5 1 pyramidal octahedral AB 4 E 2 4 2 F F Xe F F 10.1 MOLECULAR GEOMETRY Predicting Molecular Geometry 1. Draw Lewis structure for molecule. 2. Count number of lone pairs on the central atom and number of atoms bonded to the central atom. 3. Use VSEPR to predict the geometry of the molecule. What are the molecular geometries of SO 2 and SF 4 ? 8

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 rich electron poor region region F H δ - δ + DIPOLE MOMENTS  H 2 O vs CO 2  BF 3 vs NH 3  cis -C 2 H 2 Cl 2 vs trans- C 2 H 2 Cl 2 9

DIPOLE MOMENTS  H 2 O vs CO 2  BF 3 vs NH 3  cis -C 2 H 2 Cl 2 vs trans- C 2 H 2 Cl 2  NH 3 vs NF 3 10.2 10

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

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

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

What about NH 3 ? 14

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

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

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

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

HYBRIDIZATION OF 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