SLIDE 1 1
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 Valence shell electron pair repulsion (VSEPR) model:
Predict the geometry of the molecule from the electrostatic repulsions between the electron (bonding and nonbonding) pairs. AB2 2
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
B B
MOLECULAR GEOMETRY
SLIDE 2 2
Cl Cl Be AB2 2 linear linear
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB3 3
MOLECULAR GEOMETRY
SLIDE 3 3
AB2 2 linear linear
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB3 3 trigonal planar trigonal planar AB4 4
MOLECULAR GEOMETRY
AB2 2 linear linear
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB3 3 trigonal planar trigonal planar AB4 4 tetrahedral tetrahedral AB5 5
MOLECULAR GEOMETRY
SLIDE 4 4
AB2 2 linear linear
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB3 3 trigonal planar trigonal planar AB4 4 tetrahedral tetrahedral AB5 5 trigonal bipyramidal trigonal bipyramidal AB6 6
MOLECULAR GEOMETRY
SLIDE 5 5
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB3 3 trigonal planar trigonal planar AB2E 2 1 trigonal planar
MOLECULAR GEOMETRY
SLIDE 6 6
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB3E 3 1 AB4 4 tetrahedral tetrahedral tetrahedral
MOLECULAR GEOMETRY
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 H O H
MOLECULAR GEOMETRY
tetrahedral
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB5 5 trigonal bipyramidal trigonal bipyramidal AB4E 4 1 trigonal bipyramidal
MOLECULAR GEOMETRY
SLIDE 7 7
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB5 5 trigonal bipyramidal trigonal bipyramidal AB4E 4 1 trigonal bipyramidal distorted tetrahedron AB3E2 3 2 trigonal bipyramidal Cl F F F
MOLECULAR GEOMETRY
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB5 5 trigonal bipyramidal trigonal bipyramidal AB4E 4 1 trigonal bipyramidal distorted tetrahedron AB3E2 3 2 trigonal bipyramidal T-shaped AB2E3 2 3 trigonal bipyramidal I I I
MOLECULAR GEOMETRY
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB6 6
AB5E 5 1
Br F F F F F
MOLECULAR GEOMETRY
SLIDE 8 8
Class # of atoms bonded to central atom # lone pairs on central atom Arrangement of electron pairs Molecular Geometry
AB6 6
AB5E 5 1
square pyramidal AB4E2 4 2 Xe F F F F
MOLECULAR GEOMETRY
10.1
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 SO2 and SF4?
MOLECULAR GEOMETRY
SLIDE 9 9
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 and Polar Molecules
H F
electron rich region electron poor region
δ+ δ-
DIPOLE MOMENTS DIPOLE MOMENTS
H2O vs CO2 BF3 vs NH3 cis-C2H2Cl2 vs trans- C2H2Cl2
SLIDE 10 10
DIPOLE MOMENTS
H2O vs CO2 BF3 vs NH3 cis-C2H2Cl2 vs trans- C2H2Cl2 NH3 vs NF3
10.2
SLIDE 11
11
Does CH2Cl2 have a dipole moment?
DIPOLE MOMENTS
Change in electron density as two hydrogen atoms approach each other.
VALENCE BOND THEORY
SLIDE 12 12
VALENCE BOND THEORY
Covalent bond consists of pair of electrons
- f 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
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
- rbitals have very different shape from original atomic orbitals.
- 2. Number of hybrid orbitals is equal to number of pure atomic
- rbitals 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
VALENCE BOND THEORY
SLIDE 13
13
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 CH4,
SLIDE 14
14
What about NH3?
SLIDE 15
15
VALENCE BOND THEORY
Ground state orbital diagram (valence) Excitation Hybridization BF3,
Formation of sp2 Hybrid Orbitals
VALENCE BOND THEORY
Ground state orbital diagram (valence) Excitation Hybridization BeCl2,
SLIDE 16
16
Formation of sp Hybrid Orbitals
VALENCE BOND THEORY
Ground state orbital diagram (valence) Excitation Hybridization SF6,
HYBRIDIZATION OF MULTIPLE BONDS
Extra electrons not located in hybrid orbitals Sigma Bond Pi Bond
SLIDE 17
17
HYBRIDIZATION OF MULTIPLE BONDS
C2H4 (Lewis Structure) Each C is C2H4 (Lewis Structure) Each C is
HYBRIDIZATION OF MULTIPLE BONDS
SLIDE 18
18
C2H2 (Lewis Structure) Each C is
HYBRIDIZATION OF MULTIPLE BONDS HYBRIDIZATION OF MULTIPLE BONDS
SLIDE 19
19
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 CH3COOH? σ bonds = π bonds =
HYBRIDIZATION OF MULTIPLE BONDS
