02 Structure and Properties of Organic Molecules.ppt

Chapter 2Structure and Propertiesanic Molecules
Organic Chemistry, 5th EditionL. G. Wade, Jr.
Jo Blackburn
Richland College, Dallas, TX
Dallas munity College District
ã 2003, Prentice Hall
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Chapter 2
Wave Properties of Electrons
Standing wave vibrates in fixed location.
Wave function, , mathematical description of size, shape, orientation
Amplitude may be positive or negative
Node: amplitude is zero
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Chapter 2
Wave Interactions
bination of atomic orbitals
between different atoms is bond formation
on the same atom is hybridization.
Conservation of orbitals
Waves that are in phase add together.Amplitude increases.
Waves that are out of phase cancel out.  =>
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Chapter 2
Sigma Bonding
Electron density lies between the nuclei.
A bond may be formed by s-s, p-p, s-p, or hybridized orbital overlaps.
The bonding MO is lower in energy than the original atomic orbitals.
The antibonding MO is higher in energy than the atomic orbitals.  =>
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Chapter 2
H2: s-s overlap
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Chapter 2
Cl2: p-p overlap
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Constructive overlap along the same
axis forms a sigma bond.
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Chapter 2
HCl: s-p overlap
Question:
Draw the predicted shape for the bonding molecular orbital and the antibonding molecular orbital of the HCl molecule.
Answer: See bottom of page 42 in your text.
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Chapter 2
Pi Bonding
Pi bonds form after sigma bonds.
Sideways overlap of parallel p orbitals.
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Chapter 2
Multiple Bonds
A double bond (2 pairs of shared electrons) consists of a sigma bond and a pi bond.
A triple bond (3 pairs of shared electrons) consists of a sigma bond and two pi bonds.
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Chapter 2
Molecular Shapes
Bond angles cannot be explained with simple s and p orbitals. Use VSEPR theory.
Hybridized orbitals are lower in energy because electron pairs are farther apart.
Hybridization is LCAO within one atom, just prior to bonding.  =>
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Chapter 2