Unit 2.3: Chemical Bonding Sections: 10.1-10.5, 10.8 Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

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

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

Boron Trifluoride

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

Methane

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 trigonal bipyramidal trigonal bipyramidal AB5 5

Phosphorus Pentachloride

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 AB5 5 trigonal bipyramidal AB6 6 octahedral octahedral

Sulfur Hexafluoride

< bonding-pair vs. bonding- pair repulsion lone-pair vs. lone-pair lone-pair vs. bonding- <

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

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

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

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 AB3E2 3 2 trigonal bipyramidal T-shaped trigonal bipyramidal AB2E3 2 3 linear

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

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 AB5E 5 1 octahedral square pyramidal square planar AB4E2 4 2 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.

10.1 Use the VSEPR model to predict the geometry of the following molecules and ions: AsH3 OF2 C2H4

Dipole Moments and Polar Molecules electron rich region electron poor region H F 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

Bond moments and resultant dipole moments in NH3 and NF3.

10.2 Predict whether each of the following molecules has a net dipole moment: BrCl BF3 (trigonal planar) CH2Cl2 (tetrahedral)

Change in Potential Energy of Two Hydrogen Atoms as a Function of Their Distance of Separation

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

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

Formation of sp3 Hybrid Orbitals

Formation of Covalent Bonds in CH4

sp3-Hybridized N Atom in NH3 Predict correct bond angle

How do I predict the hybridization of the central atom? Draw the Lewis structure of the molecule. Count the number of lone pairs AND the number of atoms bonded to the central atom # of Lone Pairs + # of Bonded Atoms Hybridization Examples 2 sp BeCl2 3 sp2 BF3 4 sp3 CH4, NH3, H2O 5 sp3d PCl5 6 sp3d2 SF6

10.3 Determine the hybridization state of the central (underlined) atom in each of the following molecules: BeH2 AlI3 PF3 Describe the hybridization process and determine the molecular geometry in each case.

Bonding in Ethylene, C2H4 sp2 Hybridization of Carbon

Unhybridized 2pz orbital (gray), which is perpendicular to the plane of the hybrid (green) orbitals.

Bonding in Ethylene, C2H4 Pi bond (p) – electron density above and below plane of nuclei of the bonding atoms Sigma bond (s) – electron density between the 2 atoms

Another View of p Bonding in Ethylene, C2H4

Bonding in Acetylene, C2H2 sp Hybridization of Carbon

Bonding in Acetylene, C2H2

Another View of the Bonding in Acetylene, C2H2

Sigma (s) and Pi Bonds (p) 1 sigma bond Single bond Double bond 1 sigma bond and 1 pi bond Triple bond 1 sigma bond and 2 pi bonds

10.5 Describe the bonding in the formaldehyde molecule whose Lewis structure is Assume that the O atom is sp2-hybridized.

Delocalized molecular orbitals are not confined between two adjacent bonding atoms, but actually extend over three or more atoms. Example: Benzene, C6H6 Delocalized p orbitals

Bonding in the Carbonate Ion, CO32-