Welcome to 3.091Lecture 11

October 2, 2009

The Shapes of Molecules

3.091 Test #1 Wednesday, October 7, 2009

Room Assignments

A – Ha: 10-250

He - Sm: 26-100

So - ∞: 4-270

Sp2

Sp2Sp2 Z

P

Top View

C120o

120o

120o

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Sp2

Sp2 Sp2Sp2 Sp2

Sp2

Sp2

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Sp2

Sp2 Sp2

Sp2

Sp2

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Sp2

Sp2

Sp2

Sp2Sp2

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ethylene C2H4

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C CH

H

H

H

2pz 2pzz

C2H4 pi bonding

Figure 9.31

acetylene C2H2

Image by MIT OpenCourseWare.

Valence-Shell Electron-Pair-Repulsion Model

H

Li

Na

K

Rb

Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po Rn

UubRgMtHsBhSgDbRfAcRaFr Ds

Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe

Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga

B

Al Si Ar

O F Ne

He

Ge Se KrAs

C N

P S Cl

At

Br

Mg

Be

2A

3B 4B 5B 6B 7B 1B 2B

3A 4A 5A 6A 7A

8A1A

8B

Electron Configuration

Element capable of expanded octet

good e- acceptors

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S

F

F

F

F

F

F

F

F

S

NB Pair

NB Pair

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Table 9.1

Geometry

Predictedbond angles 180o 120o 109.5o 90o, 120o 90o

Linear

Electron pairs 2 3 4 5 6

Trigonal planar Tetrahedral

Electron-pair geometries for species with two to six electron pairs

Trigonal bipyramidal Octahedral

120o

90o

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Geometry

Idealized bond angles

ABn Notation AB2 AB2 AB3 AB3

ABn Notation AB4 AB4 AB5 AB6

Square planar Tetrahedral Trigonal bipyramidal Octahedral

Geometry Linear

Common molecular geometries for species with two to six bonded atomsa

Bent (V-shaped) Trigonal planar Trigonal pyramidal

180o <180o 120o <120o

Idealized bond angles

a Lone pairs are shown using a dashed line.

90o 109.5o 90o, 120o 90o

AB B AB B

AB B

B

AB

BB

..

AB B

B B..

..

..

ABB

BB

BA

B BB

B

A BB

BB

AB B

A B BB B

A

B

B

AB

B

BBB

B

AB B BB

B

B

A BB

B

B

AB

B BB

B

AB B

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Table 9.3

Overview of molecular geometries

Electron pairs

Electron pairs geometry

Molecular geometry:Zero lone pairs

Molecular geometry:One lone pair

Molecular geometry:Two lone pairs

Molecular geometry:Three lone pairs

2 3 4 5 6

120o

90o

Linear Trigonal planar Tetrahedral Trigonal bipyramidal Octahedral

Linear AB2 Trigonal planar AB3 Tetrahedral AB4 Trigonal bipyramidal AB5 Octahedral AB

AB B

AB B

AB B

B B

AB

BB

.. ..

AB

B

..

ABBB

B

.. ..

AB

BB AB

B

BB

BA

BB

BBB

B

AB

BBB

B

..

..

..

AB

BBB

....

.. A BB

B

....A BB

Bent (V-shaped) AB2

Bent (V-shaped) AB2

Linear AB2

Trigonal pyramidal AB3 Seesaw AB4 Square pyramidal AB5

Square planar AB4T-shaped AB3

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Graphite Diamond

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13IIIBIIIA

IVBIVA

VBVA

VIBVIA

VIIBVIIA

14 15 16 17VIII

0

18

0.82

1.18

Al

1.43

9.991.99/6.8

2.709 2.37

0.897322.17

293.72

10.669 1.11

1.32

12.052.32/5.38

46.44

439

439.320.705

1.49

1.06

1.28/[1.9]

17.02.63/3.63

0.628

12.43

314.640.769

0.00236*

2.62/2.9015.5

1.27/[1.85]

1.02 1.72

9.62

278.650.710

0.00270

0.99

[1.80]

18.7

3.38

10.21

121.750.479

0.000089

0.98 1.176

6.43

24.23.23/1.6411 0.520

0.0001772

2.93/2.18

0.77 0.75

17.3

0.3605

2.79472.79

1.040

0.0002598

0.73 0.2224 0.72 0.255 0.71

0.31

31.8

1.34/0.2050

0.0829

5.1930.001520

16.8

2.52/0.3956

0.3347

1.71

1.030

0.000493*

3.3179.08

0.824

0.000279

[1.35]17.1

2.26/0.557

3.41249.37

0.918

0.0002575

[1.40]14.0

2.00/0.802

0.92/[1.5]

2.07/1.10

104.60

0.709

1.2-1.5

716.72ES0.915.34

1.82/1.76

22.18

480573.21

0.274

1.026

0.984.68

- -

- - - - -

--

-

- - -

-

-

-

-

-

-

-1.56/3.03

B

Si Pwhite

α Sα

O F

Cl Ar

NeCgraphite

N

He

What's the stable form of C?

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0.77 104.60

0.709

1.2-1.5

716.72ES0.915.341.82/1.76-

-

Cgraphite

Not diamond!

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3.091SC Introduction to Solid State Chemistry Fall 2009

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