COVALENT BONDING: ORBITALS

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COVALENT BONDING ORBITALS

• HYBRIDIZATION (9.1)

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HYBRIDIZATION

• Consider methane,CH4
• C has 4 valence electrons 1s2 2s2 2p2
• This suggests that there might be two kinds of
  C-H bonds one involving a 2s e- on carbon
  pairing with the 1s on H and the other involving
  a 2p e- on carbon pairing with the 1s on H.
• Expt evidence confirms that the four C-H bonds in
  CH4 are identical and that CH4is tetrahedral.

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Figure 9.1 a b a) The Lewis Structure of the
Methane Molecule b) The Tetrahedral Molecular
Geometry of the Methane Molecule
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HYBRIDIZATION (2)

• To resolve this conflict, promote a 2s electron
  to the empty 2p orbital, then mix or hybridize
  the 2s (1) and 2p (3) orbitals to form four
  identical hybrid AOs named sp3
• These hybrid atomic orbitals overlap with the 1s
  orbital on hydrogen to form the covalent C-H bond
  (sp3 1s).
• Why do hybrids form? To minimize total energy.

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HYBRIDIZATION (3)

• Using the VSEPR rules, C has four covalent bonds
  and has tetrahedral molecular geometry. The
  H-C-H bond angle 109.5o. This agrees with
  exptal measurements (4 identical C-H bonds).
• Hybridization integrates electron configurations
  with expt measurements.
• Other hybrids sp2 (3 e pairs), sp (2), dsp3
  (5), d2sp3 (6)

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Figure 9.24 Relationship of the Number of
Effective Pairs, Their Spatial Arrangement, and
the Hybrid Orbital Set Required
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Figure 9.8 The Hybridization of the s, px, and
py Atomic Orbitals Results in the Formation of
Three sp2 Orbtitals Centered in the xy Plane
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Figure 9.9 An Orbital Energy-Level Diagram for
sp2 Hybridization
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Figure 9.11 The Sigma Bonds in Ethylene
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Figure 9.13 (a)The Orbitals Used to Form the
Bonds in Ethylene (b) The Lewis Structure for
Ethylene
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Figure 9.16 The Orbital Energy-Level Diagram for
the Formation of sp Hybrid Orbitals on Carbon
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Figure 9.20 a-d (a) The sp hybridized N atom (b)
The ? bonds in the N2 molecule (c) The two pi
bonds in N2 are formed when electron pairs are
shared between two sets of parallel p orbitals
(d) The total bonding picture of N2
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Figure 9.21 A Set of dsp3 Hybrid Orbitals on
Phosphorus Atom
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Figure 9.23 An Octahedral Set of d2sp3 Orbitals
on Sulfur Atom
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Figure 9.24 Relationship of the Number of
Effective Pairs, Their Spatial Arrangement, and
the Hybrid Orbital Set Required
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HYBRIDS AND MOLECULAR STRUCTURE

• Write Lewis structure and use VSEPR method to
  predict e pair geometry
• Select hybridization scheme this is consistent
  with VSEPR prediction (Fig 9.24)
• Identify orbital overlap
• Form multiple bonds if needed
• Determine molecular geometry

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HYBRIDS AND MULTIPLE BONDS (1)

• Use Valence Bond method to determine
  3-dimensional structure of hydrocarbons with
  double and triple bonds (planar)
• Sigma (?) or end-to-end orbital overlap bond
• Pi (?) or side-by-side orbital overlap bond
• Geometric isomers (2-butene)
• Benzene and other aromatic compounds

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HYBRIDS AND MULTIPLE BONDS (2)

• A single bond has one sigma bond.
• A double bond has one sigma bond and one pi bond.
• A triple bond has one sigma bond and two pi
  bonds.

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Problems

• 16, 18, 22, 24, 28, 32, 33