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CHAPTER TEN

CHEMICAL BONDING II:MOLECULAR GEOMETRY ANDHYBRIDIZATION OF ATOMIC

ORBITALS

MOLECULAR GEOMETRY

VSEPR

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 repulsionsbetween the electron (bonding and nonbonding) pairs.

AB2 2 0

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

B B

MOLECULAR GEOMETRY

2

Cl ClBe

AB2 2 0 linear linear

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB3 3 0

MOLECULAR GEOMETRY

3

AB2 2 0 linear linear

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB3 3 0 trigonalplanar

trigonalplanar

AB4 4 0

MOLECULAR GEOMETRY

AB2 2 0 linear linear

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB3 3 0 trigonalplanar

trigonalplanar

AB4 4 0 tetrahedral tetrahedral

AB5 5 0

MOLECULAR GEOMETRY

4

AB2 2 0 linear linear

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB3 3 0 trigonalplanar

trigonalplanar

AB4 4 0 tetrahedral tetrahedral

AB5 5 0 trigonalbipyramidal

trigonalbipyramidal

AB6 6 0

MOLECULAR GEOMETRY

5

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB3 3 0 trigonalplanar

trigonalplanar

AB2E 2 1 trigonalplanar

MOLECULAR GEOMETRY

6

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB3E 3 1

AB4 4 0 tetrahedral tetrahedral

tetrahedral

MOLECULAR GEOMETRY

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB4 4 0 tetrahedral tetrahedral

AB3E 3 1 tetrahedral trigonalpyramidal

AB2E2 2 2

HO

H

MOLECULAR GEOMETRY

tetrahedral

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB5 5 0 trigonalbipyramidal

trigonalbipyramidal

AB4E 4 1 trigonalbipyramidal

MOLECULAR GEOMETRY

7

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB5 5 0 trigonalbipyramidal

trigonalbipyramidal

AB4E 4 1 trigonalbipyramidal

distortedtetrahedron

AB3E2 3 2 trigonalbipyramidal

ClF

F

F

MOLECULAR GEOMETRY

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB5 5 0 trigonalbipyramidal

trigonalbipyramidal

AB4E 4 1 trigonalbipyramidal

distortedtetrahedron

AB3E2 3 2 trigonalbipyramidal T-shaped

AB2E3 2 3 trigonalbipyramidal

I

I

I

MOLECULAR GEOMETRY

Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB6 6 0 octahedraloctahedral

AB5E 5 1 octahedral

Br

F F

FF

F

MOLECULAR GEOMETRY

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Class

# of atomsbonded to

central atom

# lonepairs on

central atomArrangement of

electron pairsMolecularGeometry

AB6 6 0 octahedraloctahedral

AB5E 5 1 octahedral squarepyramidal

AB4E2 4 2

Xe

F F

FF

octahedral

MOLECULAR GEOMETRY

10.1

Predicting Molecular Geometry1. Draw Lewis structure for molecule.

2. Count number of lone pairs on the central atom andnumber 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

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DIPOLE MOMENTS

Bonds and molecules may be polar ornonpolar

Relative to distribution of electrons Dipole moment (µ= Q x r) Bonds

Molecule

Dipole Moments and Polar Molecules

H F

electron richregionelectron poor

region

δ+ δ-

DIPOLE MOMENTS

DIPOLE MOMENTS

H2O vs CO2

BF3 vs NH3

cis-C2H2Cl2 vs trans- C2H2Cl2

10

DIPOLE MOMENTS

H2O vs CO2

BF3 vs NH3

cis-C2H2Cl2 vs trans- C2H2Cl2 NH3 vs NF3

10.2

11

Does CH2Cl2 havea dipole moment?

DIPOLE MOMENTS

Change in electron densityas two hydrogen atomsapproach each other.

VALENCE BOND THEORY

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VALENCE BOND THEORY

Covalent bond consists of pair of electronsof opposite spin within an AO

Appears that to form bond, must haveunpaired electron

New AO--hybrid orbital Mix AO before bonding occurs Explains # of bonds and bond angles

Hybridization – mixing of two or more atomic orbitals toform a new set of hybrid orbitals.

1. Mix at least 2 nonequivalent atomic orbitals (e.g. s and p). Hybridorbitals have very different shape from original atomic orbitals.

2. Number of hybrid orbitals is equal to number of pure atomicorbitals 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

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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,

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What about NH3?

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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,

16

Formation of sp Hybrid Orbitals

VALENCE BOND THEORY Ground state orbital diagram (valence) Excitation Hybridization SF6,

HYBRIDIZATION OFMULTIPLE BONDS

Extra electrons not located in hybrid orbitals Sigma Bond

Pi Bond

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HYBRIDIZATION OFMULTIPLE BONDS

C2H4 (Lewis Structure) Each C is

C2H4 (Lewis Structure) Each C is

HYBRIDIZATION OFMULTIPLE BONDS

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C2H2 (Lewis Structure) Each C is

HYBRIDIZATION OFMULTIPLE BONDS

HYBRIDIZATION OFMULTIPLE BONDS

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Sigma (σ) and Pi Bonds (π)

Single bondDouble bondTriple bond

How many σ and π bonds are in the acetic acid(vinegar) molecule CH3COOH?

σ bonds = π bonds =

HYBRIDIZATION OFMULTIPLE BONDS