1

Five Basic Geometries

LinearTrigonal

Octahedral

Trigonal bipyramidal

Tetrahedral

2

SeF6, IF5, and XeF4

3

SeF6: Octahedron

All bond angles are 90°

4

IF5 and XeF4

IF5 XeF4

Square Pyramidal

Square Planar

The 1st lone pair can occupy any site

The 2nd lone pair is arranged opposite to the 1st

5

Octahedral Electronic Geometry

If lone pairs are incorporated into the octahedral structure, there are 2 possible new shapes

1 lone pair – Square pyramid

2 lone pairs – Square planar

6

Chemical Bonding

How are the chemical bonds formed?

Formation of a chemical bond usually involves pairing of unpaired electrons from the atoms being bound

Example – H2 molecule

H· + ·H H:H

7

BeH2

The Be atom has 2 paired electrons How does it form 2 equivalent bonds?

To answer questions like this, the valence bond theory was proposed

BeH H

8

Valence Bond Theory When an atom is nearby other

atoms, its outer shell orbitals can mix and get modified

They form a new set of orbitals that are more appropriate for bonding

This process is called hybridization

The new orbitals are therefore called hybrid orbitals

Hybrid orbitals are arranged in the same way as predicted by VSEPR

9

BeH2

Be: 1s22s2s22

sp - hybridization

10

BeH2

H H+ +Be1s

1s

sp sp

11

BF3

BF

F

F

12

BF3

B: 1s22s2s222p2p11

sp 2 - hybridization

13

BF3

+

B

3 F2p

14

CH4 and CF4

109.5°

15

C: 1s22s2s222p2p22

sp 3 - hybridization

CH4 and CF4

16

CH4

+

4

C

H

1s

17

CF4

+

4 F

C

2p

18

NH3 and NF3

NH3 NF3

107.3°

102.1°

Just like in CH4 and CF4, the orbitals are arranged in the tetrahedral fashion which means that the sp

3 hybridization takes place

One of the orbitals, however, contains a pair of electrons and is not used for bonding

19

N: 1s22s2s222p2p33 sp 3 - hybridization

NH3 and NF3

N

Four sp 3

orbitals

20

+

3

N

H

1s

NH3 and NF3

21

NH4+

+

H+

1s +

22

PF5

P: [Ne]3s3s223p3p33

sp 3d - hybridization

23

PF5

Trigonal bipyramidal electronic geometry is achieved by sp

3d - hybridization

24

SF6

S: [Ne]3s3s223p3p44

sp 3d

2 - hybridization

25

SF6

Octahedral electronic geometry is achieved by sp

3d 2 - hybridization

26

VB vs. VSEPR Theories

Regions of High

Electron Density

Electronic Geometry

Hybridization

2 Linear sp

3 Trigonal planar

sp2

4 Tetrahedral sp3

5 Trigonal bipyramidal

sp3d

6 Octahedral sp3d2

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Double Bond: C2H4

An sp 2 hybridized C atom has one

electron in each of the three sp 2 lobes

Top view of the sp

2 hybrid

Side view of the sp 2 hybrid

+ the unhybridized p orbital

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Two sp 2 hybridized C atoms plus p -orbitals in

proper orientation to form a C=C double bond

Double Bond: C2H4

29

Double Bond: C2H4

The portion of the double bond formed from the head-on overlap of the sp

2 hybrids is designated as a bond

The other portion of the double bond, resulting from the side-on overlap of the p orbitals, is designated as a bond

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A bond results from the head-on overlap of two sp hybrid orbitals

Triple Bond: C2H2

31

The unhybridized p orbitals form two bonds

Note that a triple bond consists of one and two bonds

Triple Bond: C2H2

32

Assignments & Reminders

Go through the lecture notes

Read Chapter 8 completely

Homework #5 covers Chapters 7 & 8 and is due by Oct. 31

Monday (10/31) and Tuesday (11/1) – lecture quiz #5 (Chapter 8)