04. Hybridization 2010

Chemical Bonds

Chemical bonds

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 Information  Introduction: What is Organic Chemistry ?  Structures: Ch. 1.3  Alkanes: Ch. 2.1-2.3  Functional groups: Ch. 2.5-2.13  Chemical Bonding & Lewis Structures: Ch. 1.4-1.6  Formal Charges and Resonance: Ch. 1.7-1.8  VSEPR Theory Ch. 1.16  Hybridization Ch. 1.11-1.15 CHEM 212

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Chemical Bonding  Bonds can be z Covalent. Ex.: CH4 ÎAtoms achieve octets by sharing of valence electrons H H H

C

H

C H

H

H

H

z Ionic Ex. NaCl, LiF ÎOctet rule: Lithium loses an electron and becomes positively charged ÎFluoride gains an electron and becomes negatively charged ÎThe charged lithium and fluoride form a strong ionic bond

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Valence Bond Theory  The covalent bond results from an overlap of atomic

orbitals containing one unpaired electron each  Pauling (Nobel in Chemistry 1954 in Peace 1962)  Aufbau z orbitals are filled so that those of lowest energy are filled first

 Pauli z a maximum of two electrons with paired spins may be placed in each

orbital

 Hund z With orbitals of equal energy, one electron (unpaired spins) is added to

each until each contains one electron

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The Covalent Bond - Pauling  Sharing of unpaired electrons

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H

H

1s

1s

1s

1s

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The Covalent Bond - Pauling  Shairing of unpaired electrons

H

H

1s

1s

σ bond CHEM 212

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H2  1s + 1s = σ

H

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H

H2

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F2  p-p Overlap

F 1s

2s

2p

1s

2s

2p

F

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He2?  No unpaired electrons  This molecule cannot exist

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He

He

1s

1s

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HF?  Unpaired electrons  s-p overlap

F 1s

2s

2p

H 1s

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HF  Fluoride is more electronegative than H:  polarized bond

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Single bonds  Carbon atom

jump

C 1s

2s

2p

H 1s

 4 sp3 electrons

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Hybridization  2s + 2px+ 2py+ 2pz= 4 sp3 e-

C 1s

2s

2p

Hybri dization

sp3

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Methane  Hybridization

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Methane  Bond formation

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Methane H  Lewis Structure

H

C

H

H  Geometry (VSEPR)

 Bonding (Valence bond theory): 4

equivalent σ bonds

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Multiple bonds  Ethylene

H

H C

z Lewis structure

H

C H

z VSEPR: 2 trigonal planar carbons

z Valence bond theory: 1σ and 1π

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Hybridization

C 2s

2p

sp2

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p

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Ethylene

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Ethylene

sp2

3 σ bonds

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p

1 π bond

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π bond

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Triple bond  Acetylene (ethyne) z Lewis structure

H

C

C

H

z VSEPR: 2 linear carbons

z Valence bond theory: 1σ and 2π

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Triple Bonds

C 2s

2p

sp

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p

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Acetylene

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Acetylene H

σ bond

s

sp

p

sp

p

σ bond

H

C

C

H

H s

σ bond CHEM 212

2 π bonds

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The electron configuration shown below represents

1s 2sp3 2sp3 2sp3 2sp3 1. 2. 3. 4. 5.

the ground state of boron. the sp3 hybridized state of carbon the sp3 hybridized state of nitrogen the ground state of carbon. an excited state of carbon. 0%

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1

0% 2

0%

0%

3

4

0% 5

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