Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals Chapter 10 Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

TOPICS MOLECULAR GEOMETRY DIPOLE MOMENT FOR A MOLECULE HYBRID ORBITALS

MOLECULAR GEOMETRY NEED LEWIS STRUCTURE FOR A MOLECULE. WILL USE VSEPR MODEL TO DETERMINE MOLECUAR GEOMETRY.

Predicting Molecular Geometry Draw Lewis structure for molecule. Count number of lone pairs on the central atom and number of atoms bonded to the central atom. Use VSEPR to predict the geometry of the molecule. What are the molecular geometries of SO2 and SF4? S F S O AB4E AB2E distorted tetrahedron bent

VSEPR PATTERNS

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 central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB2 2 linear linear B

0 lone pairs on central atom Cl Be 2 atoms bonded to central atom

Predicting Molecular Geometry Draw Lewis structure for molecule. Count number of lone pairs on the central atom and number of atoms bonded to the central atom. Use VSEPR to predict the geometry of the molecule. What are the molecular geometries of SO2 and SF4? S F S O AB4E AB2E distorted tetrahedron bent

VSEPR MODEL Need a Lewis Structure for the model. Need to know the number of bonded pairs and non bonded pairs. Arrange valence electrons so have a three dimensional shape where valence electrons don’t repulse or have a minimal repulsion.

VSEPR MODEL NOTES Double or triple bonds are treated like single bonds. Find pattern for molecule. A certain pattern will have a certain shape.

Arrangement of electron pairs VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry trigonal planar trigonal planar AB3 3 trigonal planar AB2E 2 1 bent

VSEPR trigonal bipyramidal trigonal bipyramidal AB5 5 AB4E 4 1 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry trigonal bipyramidal trigonal bipyramidal AB5 5 AB4E 4 1 trigonal bipyramidal distorted tetrahedron trigonal bipyramidal AB3E2 3 2 T-shaped

Arrangement of electron pairs VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB2 2 linear linear trigonal planar trigonal planar AB3 3

Arrangement of electron pairs VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB2 2 linear linear AB3 3 trigonal planar AB4 4 tetrahedral tetrahedral

DIPOLE MOMENT AND POLAR MOLECULES u = Q x r

Dipole Moments and Polar Molecules H F electron rich region electron poor region d+ d- m = Q x r Q is the charge r is the distance between charges 1 D = 3.36 x 10-30 C m

Behavior of Polar Molecules field off field on

Dipole Moments For Molecules Write Lewis Structure if not provided. Apply VSEPR model to determine shape of molecule. Decide if molecule is symmetrical or nonsymmetrical.

Dipole Moments For Molecules Decide if bonds are polar versus nonpolar. If polar covalent bonds are equal and opposite in a symmetrical molecule, dipole moments will cancel and molecule will be nonpolar.

Dipole Moments For Molecules If polar bonds don’t have the same dipole moment or are not equal and opposite, molecule will be polar

The Electronegativities of Common Elements

Which of the following molecules have a dipole moment? H2O, CO2, SO2, and CF4 O H S O dipole moment polar molecule dipole moment polar molecule C F C O no dipole moment nonpolar molecule no dipole moment nonpolar molecule

Does CH2Cl2 have a dipole moment?

COVALENT BONDS AND ORBITALS VALENCE ELECTRONS ARE IN S, P, D, F SUBSHELLS. QUANTUM MECHANICS CALULATES THAT SUBSHELLS HAVE SHAPES. COVALENT BONDS HAVE SHAPES.

l = 0 (s orbitals) l = 1 (p orbitals)

ml = -1, 0, or 1 3 orientations is space

Sharing of two electrons between the two atoms. How does Lewis theory explain the bonds in H2 and F2? Sharing of two electrons between the two atoms. Bond Enthalpy Bond Length H2 F2 436.4 kJ/mol 150.6 kJ/mol 74 pm 142 pm Overlap Of 2 1s 2 2p Valence bond theory – bonds are formed by sharing of e- from overlapping atomic orbitals.

Change in electron density as two hydrogen atoms approach each other.

Valence Bond Theory and NH3 N – 1s22s22p3 3 H – 1s1 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 NH3 be? If use the 3 2p orbitals predict 90o Actual H-N-H bond angle is 107.3o

Hybridization – mixing of two or more atomic orbitals to form a new set of hybrid orbitals. Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybrid orbitals have very different shape from original atomic orbitals. Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process. Covalent bonds are formed by: Overlap of hybrid orbitals with atomic orbitals Overlap of hybrid orbitals with other hybrid orbitals

Formation of sp Hybrid Orbitals

Formation of sp2 Hybrid Orbitals

Arrangement of electron pairs VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry trigonal planar trigonal planar AB3 3 trigonal planar AB2E 2 1 bent

Arrangement of electron pairs VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB4 4 tetrahedral tetrahedral trigonal pyramidal AB3E 3 1 tetrahedral

Arrangement of electron pairs VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB4 4 tetrahedral tetrahedral AB3E 3 1 tetrahedral trigonal pyramidal AB2E2 2 2 tetrahedral bent

Arrangement of electron pairs VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry AB6 6 octahedral square pyramidal AB5E 5 1 octahedral

Predicting Molecular Geometry Draw Lewis structure for molecule. Count number of lone pairs on the central atom and number of atoms bonded to the central atom. Use VSEPR to predict the geometry of the molecule. What are the molecular geometries of SO2 and SF4? S F S O AB4E AB2E distorted tetrahedron bent

VSEPR MODEL Need a Lewis Structure for the model. Need to know the number of bonded pairs and non bonded pairs. Arrange valence electrons so have a three dimensional shape where valence electrons don’t repulse or have a minimal repulsion.

VSEPR MODEL NOTES Double or triple bonds are treated like single bonds. Find pattern for molecule. A certain pattern will have a certain shape.

Arrangement of electron pairs VSEPR Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry trigonal planar trigonal planar AB3 3 trigonal planar AB2E 2 1 bent

VSEPR trigonal bipyramidal trigonal bipyramidal AB5 5 AB4E 4 1 Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry trigonal bipyramidal trigonal bipyramidal AB5 5 AB4E 4 1 trigonal bipyramidal distorted tetrahedron trigonal bipyramidal AB3E2 3 2 T-shaped

DIPOLE MOMENT AND POLAR MOLECULES u = Q x r

Dipole Moments and Polar Molecules H F electron rich region electron poor region d+ d- m = Q x r Q is the charge r is the distance between charges 1 D = 3.36 x 10-30 C m

Behavior of Polar Molecules field off field on

Dipole Moments For Molecules Write Lewis Structure if not provided. Apply VSEPR model to determine shape of molecule. Decide if molecule is symmetrical or nonsymmetrical.

Dipole Moments For Molecules Decide if bonds are polar versus nonpolar. If polar covalent bonds are equal and opposite in a symmetrical molecule, dipole moments will cancel and molecule will be nonpolar.

Dipole Moments For Molecules If polar bonds don’t have the same dipole moment or are not equal and opposite, molecule will be polar

Which of the following molecules have a dipole moment? H2O, CO2, SO2, and CF4 O H S O dipole moment polar molecule dipole moment polar molecule C F C O no dipole moment nonpolar molecule no dipole moment nonpolar molecule

Does CH2Cl2 have a dipole moment?

COVALENT BONDS AND ORBITALS VALENCE ELECTRONS ARE IN S, P, D, F SUBSHELLS. QUANTUM MECHANICS CALULATES THAT SUBSHELLS HAVE SHAPES. COVALENT BONDS HAVE SHAPES.

l = 0 (s orbitals) l = 1 (p orbitals)

ml = -1, 0, or 1 3 orientations is space

Sharing of two electrons between the two atoms. How does Lewis theory explain the bonds in H2 and F2? Sharing of two electrons between the two atoms. Bond Enthalpy Bond Length H2 F2 436.4 kJ/mol 150.6 kJ/mol 74 pm 142 pm Overlap Of 2 1s 2 2p Valence bond theory – bonds are formed by sharing of e- from overlapping atomic orbitals.

Change in electron density as two hydrogen atoms approach each other.

Valence Bond Theory and NH3 N – 1s22s22p3 3 H – 1s1 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 NH3 be? If use the 3 2p orbitals predict 90o Actual H-N-H bond angle is 107.3o

Hybridization – mixing of two or more atomic orbitals to form a new set of hybrid orbitals. Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybrid orbitals have very different shape from original atomic orbitals. Number of hybrid orbitals is equal to number of pure atomic orbitals used in the hybridization process. Covalent bonds are formed by: Overlap of hybrid orbitals with atomic orbitals Overlap of hybrid orbitals with other hybrid orbitals

Formation of sp Hybrid Orbitals

Formation of sp2 Hybrid Orbitals