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Chapter 9 Chemical Bonding Theories

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Chapter 9 Chemical Bonding ... 1/24/2006 8:53:10 PM ... Arial Calibri Symbol Default Design Adobe Photoshop Image Chapter 9 Chemical Bonding Theories Slide 2 Sigma (s – PowerPoint PPT presentation

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Title: Chapter 9 Chemical Bonding Theories


1
Chapter 9Chemical Bonding Theories
  • Valence Bond Theory Uses Lewis Structures
  • Bonds form using shared electrons between
    overlapping orbitals on adjacent atoms.
  • Orbitals arrange around central atom to avoid
    each other.
  • Two types of bonds sigma and pi.
  • Molecular Orbital Theory Uses MO Diagrams
  • Orbitals on atoms mix to make molecular
    orbtials, which go over 2 or more atoms.
  • Two electrons can be in an orbital.
  • Orbitals are either bonding, antibonding, or
    nonbonding.
  • Bonds are either sigma or pi.

2
Sigma (s) Bonding
  • Orbitals on bonding atoms overlap directly
    between bonding atoms

Between s orbitals
Between p orbitals
3
Sigma (s) Bonding
  • Consider VSEPR Shapes and bonding

4
Whats wrong with this picture?
  • Atoms bond by having their
  • valence orbitals overlap

5
2pz 2px 2py
2s
Orbitals in CH4
Orbitals on C
Orbitals dont go in same directions as atomic
orbitals.
6
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7
2pz 2px 2py
2s
Orbitals in CH4
Orbitals dont go in same directions as atomic
orbitals.
Conclusion Atomic orbitals change shape when
they make molecules.
8
Hybrid Orbitals
  • Atomic valence orbitals combine and mix to form
    new Hybrid Orbitals
  • Hybrid orbitals go in the VSEPR electron geometry
    directions.

9
Types of Hybrid Orbitals
10
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11
Types of Hybrid Orbitals 2 Pairs
12
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13
Types of Hybrid Orbitals 3 Pairs
14
Types of Hybrid Orbitals 4 Pairs
15
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16
Hybrid orbitals used for sigma bonds and lone
pairs.Unhybridized p orbitals used for pi
bonds, or they are empty.
17
Sigma Bonding
  • Orbitals overlap directly between two nuclei

18
NH3
19
CH2O
20
Sigma vs. Pi Bonding
Sigma Bonding involves hybrid orbitals and/or H
1s orbitals. Pi bonding involves unhybridized p
orbitals.
21
Pi Bond Formation
22
Bonding in Ethene
23
Bonding in Acetylene
24
Bonding in Formaldehyde
25
Bonding in Benzene
26
Advanced Allene
Each end carbon is a flat trigonal. Are they
co-planar or perpendicular?
27
Bonding in Allene
28
Conformations vs. Isomers
  • Isomers Molecules with same formula but
    different structure
  • Conformers Different temporary shapes of the
    same molecule

29
Bond Rotations
  • CAN happen around single bonds
  • Cannot happen around double bonds

30
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31
Cis-Trans Isomerization
  • When two groups are on a side of a molecule.

cis
trans
32
Can these molecules have cis-trans isomers?
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