8/10/2019 Ch09 Brady

1/51

8/10/2019 Ch09 Brady

2/51

Index

9.1. Molecules are three-dimensional with shapes that arebuilt from five basic arrangements

9.2. Molecular shapes are predicted using the VSEPR model9.3. Molecular symmetry affects the polarity of molecules9.4. Valence bond theory explains bonding as an overlap of

orbitals9.5. Hybrid orbitals are used to explain experimental

molecular geometries9.6. Hybrid orbitals can be used to explain multiple bonds

9.7. Molecular orbital theory explains bonding as constructiveinterference of atomic orbitals9.8. Molecular orbital theory uses delocalized orbitals to

describe molecules with resonance structure

8/10/2019 Ch09 Brady

3/51

9.1 Molecules are three-dimensional with shapes that are built from five basicarran ements

3

The Five Basic Electron Arrangements

ElectronDomains

Shape Electron PairGeometry

2 linear

3 trigonal planar

4 tetrahedral

8/10/2019 Ch09 Brady

4/51

9.1 Molecules are three-dimensional with shapes that are built from five basicarran ements

4

The Five Basic Electron Arrangements (Cont.)

Electron Domains Shape Electron Pair Geometry

5 trigonal bipyramidal

has equatorial and axial

positions.

6 octahedral

has equatorial and axialpositions

8/10/2019 Ch09 Brady

5/51

9.1 Molecules are three-dimensional with shapes that are built from five basicarran ements

5

Learning Check:Identify The Electron Pair Geometry For Each Center

tetrahedral tetrahedral Trigonal

bipyramidal

8/10/2019 Ch09 Brady

6/51

9.1 Molecules are three-dimensional with shapes that are built from five basicarran ements

6

Your Turn!

What is the electron pair geometry for C in CO 2?A. linearB. planar triangularC. tetrahedral

D. trigonal bipyramidalE. octahedral

8/10/2019 Ch09 Brady

7/51

9.2 Molecular shapes are predicted using the VSEPR model 7

Bonding Domains And Non-bonding Domains

Bonding domains are sharedbetween nuclei

Non-bonding domains are notshared between nuclei-they exert agreater electrical field

Repulsion leads non-bondingdomains to occupy larger space

The basic shapes are distorted bynon-bonding domains to create the molecular geometry

8/10/2019 Ch09 Brady

8/51

9.2 Molecular shapes are predicted using the VSEPR model 8

Trigonal Planar Molecular Geometries

Bonding Domains Non-bondingDomains

MolecularGeometry

3 0 trigonal planar

2 1 bent

8/10/2019 Ch09 Brady

9/51

9.2 Molecular shapes are predicted using the VSEPR model 9

Tetrahedral Molecular geometries

8/10/2019 Ch09 Brady

10/51

9.2 Molecular shapes are predicted using the VSEPR model 10

Trigonal Bipyramidal

Equatorial (e)positions aresubstituted first

This is becausethe e,e bondangles are 120 ,while a,e bondangles are only90

8/10/2019 Ch09 Brady

11/51

9.2 Molecular shapes are predicted using the VSEPR model 11

Octahedral Geometries

All bond anglesare 90

Axial positionsare substitutedfirst

8/10/2019 Ch09 Brady

12/51

9.2 Molecular shapes are predicted using the VSEPR model 12

Learning Check:

Identify the molecular geometry for each center

Trigonal

pyramidal

Non-linear,

bentLinear

8/10/2019 Ch09 Brady

13/51

9.2 Molecular shapes are predicted using the VSEPR model 13

Your Turn!

Which require more space?A. bond pairsB. lone pairsC. both are the same

8/10/2019 Ch09 Brady

14/51

9.2 Molecular shapes are predicted using the VSEPR model 14

Your Turn!

Which bond angles are closer in a trigonalbipyramidal structure (a= axial; e=equatorial)?

A. a-aB. a-e

C. e-eD. they are all the same

8/10/2019 Ch09 Brady

15/51

9.2 Molecular shapes are predicted using the VSEPR model 15

Your Turn!

What is the molecular geometry of C in CH 4?A. LinearB. Square planarC. Square pyramidal

D. TetrahedralE. None of these

8/10/2019 Ch09 Brady

16/51

9.3 Molecular symmetry affects the polarity of molecules 16

Polar Molecules Are Asymmetric

To determine the polarity, draw the structure usingthe proper molecular geometry

Draw the bond dipoles If they cancel, the molecule is non-polar If the molecule has uneven dipole distribution, it is

polar

8/10/2019 Ch09 Brady

17/51

9.3 Molecular symmetry affects the polarity of molecules 17

Learning Check:

Polar or non-polar?

polar Non-polarpolar

8/10/2019 Ch09 Brady

18/51

9.3 Molecular symmetry affects the polarity of molecules 18

Your Turn!

CH 2ClCH 2Cl (freon-150) is likely to be:A. PolarB. non-polarC. cannot tell

8/10/2019 Ch09 Brady

19/51

9.3 Molecular symmetry affects the polarity of molecules 19

Your Turn!

Benzoyl peroxide (used in common acnemedications) is likely to be:

A. polarB. non-polar

C. cannot tell

8/10/2019 Ch09 Brady

20/51

9.4 Valence bond theory explains bonding as an overlap of atomic orbitals 20

Valence Bond Theory

H2 bonds form because atomic valence orbitalsoverlap

HF involves overlaps between the s orbital on Hand the 2p orbital of F

1s 1s

1s 2s 2p

8/10/2019 Ch09 Brady

21/51

9.4 Valence bond theory explains bonding as an overlap of atomic orbitals 21

VB Theory And H 2S

Assume that theunpaired e - in S and Hare free to form apaired bond

We may assume thatthe H-S bond formsbetween an s and a porbital

8/10/2019 Ch09 Brady

22/51

9.4 Valence bond theory explains bonding as an overlap of atomic orbitals 22

Your turn!

According to VB Theory:Which type of overlap does not occur in BH 3?A. s-sB. s-p

C. p-pD. none of these

8/10/2019 Ch09 Brady

23/51

9.4 Valence bond theory explains bonding as an overlap of atomic orbitals 23

Your turn!

According to VB Theory:Which orbitals overlap in the formation of NH 3?A. s-sB. s-p

C. p-pD. none of these

8/10/2019 Ch09 Brady

24/51

9.4 Valence bond theory explains bonding as an overlap of atomic orbitals 24

Difficulties With VB Theory So Far:

Most experimental bond angles do not supportthose predicted by mere atomic orbital overlap

For example: C 1s 22s22p 2 and H 1s 1

Experimental bond angles in methane are 109.5

and all are the same p orbitals are 90 apart, and not all valence e - inC are in the p orbitals

How can multiple bonds form?

8/10/2019 Ch09 Brady

25/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 25

Hybridization

The mixing of atomic orbitals to allow formationof bonds that have realistic bond angles

The new shapes that result are called hybridorbitals

The number of hybrid orbitals required = thenumber of bonding domains + the number ofnon-bonding domains on the atom

8/10/2019 Ch09 Brady

26/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 26

What Shall We Call These New Orbitals?

Since we have annexed the spaces previouslydefined by atomic orbitals, we name the hybrid asa combination of the orbitals used to form the newhybrid

One atomic orbital is used for every hybrid formed(orbitals are conserved)

8/10/2019 Ch09 Brady

27/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 27

Hybrids From s & p Atomic Orbitals takeVSEPR Geometry

Hybrid Atomic

OrbitalsUsed

Electron

Geometry

sp3 s + p x + p y+ p z

Tetrahedral,bond angles

109.5 sp2 s + p x + p y Trigonal

planar, bondangles 120

sp s + p x Linear,bond angles180

8/10/2019 Ch09 Brady

28/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 28

Learning Check:

Identify The Hybrid Orbitals In The Following, Based

On Their VSEPR Geometry

8/10/2019 Ch09 Brady

29/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 29

Determining hybridization:

1. expand all valence electrons within the valenceenergy level. For C, for example this means:

2s 2p _ ___ [He]2s 2 2p1

Becomes:

2s

2p

_

_

__

8/10/2019 Ch09 Brady

30/51

8/10/2019 Ch09 Brady

31/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 31

Hybridization (sp 3)

3. Now analyze the atomic orbital needs. You will needto use one atomic orbital for every hybrid orbital .

For C in CH 4 we will need 4 hybrid orbitals. 2s 2p _ _ Thus, we will need to use all valence level atomic

orbitals available to us. (2s 2p _ _ ) S + p + p + p 4 new equivalent sp 3 orbitals.

H

HH

H

C

8/10/2019 Ch09 Brady

32/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 32

Bonding in CH 4

The 4 hybrid orbitals areevenly distributed around

the C The H s-orbitals overlap

the sp 3 hybrid orbitals toform the bonds.

H

HH

H

8/10/2019 Ch09 Brady

33/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 33

s & p hybrid shapes

8/10/2019 Ch09 Brady

34/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 34

Your Turn!

In the compound CH 3OH, what is the expectedhybridization on O?

A. spB. sp 2

C. sp 3

D. O does not hybridize

8/10/2019 Ch09 Brady

35/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 35

Expanded Octet Hybridization

Can be predicted from the geometry as well In these situations, d orbitals are be needed to

provide room for the extra electrons One d orbital is added for each pair of electrons in

excess of the standard octet

8/10/2019 Ch09 Brady

36/51

9.5 Hybrid orbitals are used to explain experimental molecular geometries 36

Expanded Octet hybridization

8/10/2019 Ch09 Brady

37/51

9.6 Hybrid orbitals can be used to describe multiple bonds 37

Bonding Types

Two types of bonds result fromorbital overlap:

sigma bondsfrom head-on overlaplie along the bond axisaccount for the first bond

pi bondsfrom lateral overlap by adjacent p ord orbitals

pi bonds are perpendicular to bondaxisaccount for the second and thirdbonds in a multiple bond

8/10/2019 Ch09 Brady

38/51

9.6 Hybrid orbitals can be used to describe multiple bonds 38

Hybridization of C in CH 2O O

H HC

1. Expand all valence electrons within the same energy level.

For C, for example this means: 2s 2p _ ___ [He]2s 2 2p 1

Becomes:

2s 2p _ _ __

8/10/2019 Ch09 Brady

39/51

9.6 Hybrid orbitals can be used to describe multiple bonds 39

Hybridization of C in CH 2O O

H HC

2. Now analyze the bonding and lone pair needs.You will need to use one hybrid orbital forevery attached atom and one for every lone pair.

For C in CH 2O we see that there are 3 attached atomsand no lone pairs on C. Thus we will need 3 hybridorbitals.

8/10/2019 Ch09 Brady

40/51

9.6 Hybrid orbitals can be used to describe multiple bonds 40

sp2 Hybridization

3. Now analyze the atomic orbital needs. You willneed to use one atomic orbital for every hybrid

orbital.For C in CH 2O we will need 3 hybrid orbitals.2s 2p _ _Thus, we will need to use 3 valence level atomicorbitals available to us, and one of the p orbitals willremain.(2s 2p _ ) _

s + p + p 3 new sp2

orbitals.We are left with one unhybridized orbital.

8/10/2019 Ch09 Brady

41/51

9.6 Hybrid orbitals can be used to describe multiple bonds 41

Now analyze the O:

[He] 2s 2 2p 2 (2s 2p _ ) _

The O is has one bonding domain and 2 non-bonding domains, hence it will require threehybrid orbitals.

No expansion needed, as one unpaired e - isavailable to bond. Use 3 atomic orbitals to makethe new hybrids, sp 2. (2s 2p _ ) _

Again we are left with one unhybridized porbital

O

H HC

8/10/2019 Ch09 Brady

42/51

9.6 Hybrid orbitals can be used to describe multiple bonds 42

Pi Bonding

8/10/2019 Ch09 Brady

43/51

9.6 Hybrid orbitals can be used to describe multiple bonds 43

H C C H

Each C has atriple bond

and a singlebond

Requires 2

hybridorbitals, sp

unhybridized p orbitalsused to formthe pi bond

8/10/2019 Ch09 Brady

44/51

9.6 Hybrid orbitals can be used to describe multiple bonds 44

Your Turn!

Consider a molecule of CH 3CO 2H:How many pi bonds are there in the molecule?A. 1B. 2

C. 3D. 4E. There are none

8/10/2019 Ch09 Brady

45/51

9.7 Molecular orbital theory explains bonding as constructive interference of atomicorbitals

45

Molecular Orbital Theory

Modification of VB theory that considers that the orbitalsmay exhibit interference.

Waves may interfere constructively or destructively Bonding orbitals stabilize, antibonding destabilize.

8/10/2019 Ch09 Brady

46/51

9.7 Molecular orbital theory explains bonding as constructive interference of atomicorbitals

46

MO diagrams

Show atomic energy level diagram for each atom Show molecular orbitals (bonding and

antibonding*) 1 MO for each Atomic orbital. Show electron occupancy of the orbitals.

8/10/2019 Ch09 Brady

47/51

9.7 Molecular orbital theory explains bonding as constructive interference of atomicorbitals

47

Filling MO diagrams

1. Electrons fill the lowest-energy orbitals that areavailable.

2. No more than two electrons, with spins paired,can occupy any orbital.

3. Electrons spread out as much as possible, withspins unpaired, over orbitals that have the sameenergy.

4. Bond order = e - in bonding orbital-e - innonbonding orbitals.

8/10/2019 Ch09 Brady

48/51

9.7 Molecular orbital theory explains bonding as constructive interference of atomicorbitals

48

Diatomic MO diagrams differ by group

A) I - V B) VI-VIIIA

8/10/2019 Ch09 Brady

49/51

9.7 Molecular orbital theory explains bonding as constructive interference of atomicorbitals

49

MO diagrams

Draw the expected MO diagram for: O2

BH

He 2

Which are not likely to exist, and why?

8/10/2019 Ch09 Brady

50/51

9.8 Molecular orbital theory uses delocalized orbitals to describe molecules withresonance structures

50

Delocalized Electrons

Lewis structures use resonance to explain that theactual molecule appears to have several equivalent

bonds, rather than different possible structures MO theory shows the electrons being delocalized

in the structure

8/10/2019 Ch09 Brady

51/51