Welcome to Chemistry 7!...Chapter 11 Theories of Covalent Bonding Chapter Outline Valence Bond (VB)...
Transcript of Welcome to Chemistry 7!...Chapter 11 Theories of Covalent Bonding Chapter Outline Valence Bond (VB)...
Announcement
March 19, Thursday
◦ LT#3: 120 points: 40 items MC x 2.5 pts
each + 2 PS items x 10 pts each
◦ 6-7:30 PM
◦ Schmitt Hall C-114
◦ Coverage: Chapters 7-11
March 20, Friday
◦ Quiz # 10, 11, 12
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Electron and Molecular Geometry
Electron geometry: geometry of all electron groups
Molecular geometry: geometry of only the atoms bonded to the central atom
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Bond Polarity, Bond Angle, and
Dipole Moment
Overall molecular polarity depends on both
shape and bond polarity.
A molecule is polar if
- it contains one or more polar bonds and
- the individual bond dipoles do not cancel.
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C (EN = 2.5) and
O (EN = 3.5) H (EN = 2.1) and
O (EN = 3.5)
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Molecules with the same shape may have
different polarities.
CCl4
Bonds are polar, but
individual bond
polarities cancel.
CHCl3
Bond polarities do
not cancel. This
molecule is polar.
Bond Polarity, Bond Angle, and Dipole Moment
Chapter 11 Theories of Covalent Bonding
Chapter Outline
Valence Bond (VB) Theory and Orbital
Hybridization
Modes of Orbital Overlap and the
Types of Covalent Bonds
Excluded Topic:
11.3 Molecular Orbital (MO) Theory
and Electron Delocalization
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Valence Bond Theory
A covalent bond forms when the
orbitals of two atoms overlap and a
pair of electrons occupy the overlap
region.
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Shared space is occupied
by 2 e-, which have
opposite spins.
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Bonding in HF
Bonding in F2
The greater the extent of orbital overlap, the
stronger the bond.
Bonding in carbon presents a problem as
combining atomic orbitals fails. Valence
Bond Theory solves this by allowing the
blending or mixing of pure atomic orbitals in
a process called hybridization.
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Pure atomic
orbitals
sp3
hybridized
orbitals
hybridization
sp3 sp3 sp3 sp3
Hybridization combines or mixes different
numbers of pure atomic orbitals that match
one of the VSEPRT geometries.
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s-orbital + p-orbital 2 sp hybrid
orbitals
2 superimposed sp
hybrid orbitals
s-orbital + 2 p-orbitals 3 sp2 hybrid
orbitals
trigonal
planar
Hybridization combines or mixes different
numbers of pure atomic orbitals that match
one of the VSEPRT geometries.
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s-orbital + 3 p-orbital 4 sp3 hybrid
orbitals tetrahedral
Characteristics of Hybrid
Orbitals
1. The number of hybrid orbitals obtained equals
the number of atomic orbitals mixed.
2. The name and shape of a “hybrid orbital”
varies with the types of atomic orbitals mixed.
3. Each hybrid orbital has a specific geometry
that matches one of five VSEPRT shapes.
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sp Hybridization
Show the bonding scheme and hybridized
orbitals used in BeCl2.
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After hybridization,
central atom now has
2 pure p-orbitals and
2 sp hybrids.
s + p hybridization 2 sp
sp Hybridization
Show the bonding scheme and hybridized
orbitals used in BeCl2.
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After hybridization,
central atom now has
2 pure p-orbitals and
2 sp hybrids.
s + p hybridization 2 sp
sp Hybridization
Show the bonding scheme and hybridized
orbitals used in BeCl2.
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2 sp orbitals
2 pure p-orbitals
Linear
sp2 Hybridization (ie BF3)
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Trigonal
Planar
sp3 Hybridization (ie CH4)
17 Tetrahedral
sp3 Hybridization (ie NH3)
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Trigonal
pyramidal
sp3 Hybridization (ie H2O)
19 Bent
sp3d Hybridization (ie PCl5)
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Trigonal
bipyramidal
sp3d2 Hybridization (ie SF6)
21 Octahedral
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Learning Check
Determine the VSEPRT geometry,
bond angle, and hybridization of each
indicated atom in the following
molecule.
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Types of Covalent Bonds
1. A sigma (σ) bond is formed by end-to-end overlap of orbitals.
◦ All single bonds are σ bonds.
2. A pi (p) bond is formed by sideways overlap of orbitals.
◦ A p bond is weaker than a σ bond because sideways overlap is less effective than end-to-end overlap.
◦ A double bond consists of one σ bond and one p bond.
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Double Bond (ie ethylene)
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unhybridized 2p orbitals
Triple Bond (ie acetylene)
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Each C is sp hybridized and has
two unhybridized p orbitals.
Announcement
March 19, Thursday
◦ LT#3: 120 points: 40 items MC x 2.5 pts
each + 2 PS items x 10 pts each
◦ 6:00-7:30 PM
◦ Schmitt Hall C-114
◦ Coverage: Chapters 7-11
March 20, Friday
◦ Quiz # 10, 11, 12
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