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Chapter 9 Covalent Bonding: Orbitals

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Chapter 9 Covalent Bonding: Orbitals Hybridization The mixing of atomic orbitals to form special orbitals for bonding. The atoms are responding as needed to give the ... – PowerPoint PPT presentation

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Title: Chapter 9 Covalent Bonding: Orbitals


1
Chapter 9Covalent Bonding Orbitals
  • Hybridization
  • The mixing of atomic orbitals to form special
    orbitals for bonding.
  • The atoms are responding as needed to give the
    minimum energy for the molecule.

2
The Valence Orbitals on a Free Carbon Atom 2s,
2px, 2py, and 2pz
3
The Formation of sp3 Hybrid Orbitals
4
An Energy-Level Diagram Showing the Formation of
Four sp3 Orbitals
5

Tetrahedral Set of Four sp3 Orbitals
6
The Nitrogen Atom in Ammonia is sp3 Hybridized
7
sp3 Hybridization
  • The experimentally known structure of CH4
    molecule can be explained if we assume that the
    carbon atom adopts a special set of atomic
    orbitals. These new orbital are obtained by
    combining the 2s and the three 2p orbitals of the
    carbon atom to produce four identically shaped
    orbital that are oriented toward the corners of a
    tetrahedron and are used to bond to the hydrogen
    atoms.
  • Whenever a set of equivalent tetrahedral atomic
    orbitals is required by an atom, this model
    assumes that the atom adopts a set of sp3
    orbitals the atom becomes sp3 hybridized.

8
The Hybridization of the s, px, and py Atomic
Orbitals
9
An Orbital Energy-Level Diagram for sp2
Hybridization
10
  • A sigma (?) bond centers along the internuclear
    axis.
  • A pi (?) bond occupies the space above and below
    the internuclear axis.

11
An sp2 Hybridized C Atom
12
The s Bonds in Ethylene
13
Sigma and Pi Bonding
14
The Orbitals for C2H4
15
When One s Orbital and One p Orbital are
Hybridized, a Set of Two sp Orbitals Oriented at
180 Degrees Results
16
The Hybrid Orbitals in the CO2 Molecule
17
The Orbital Energy-Level Diagram for the
Formation of sp Hybrid Orbitals on Carbon
18
The Orbitals of an sp Hybridized Carbon Atom
19
The Orbital Arrangement for an sp2 Hybridized
Oxygen Atom
20
The Orbitals for CO2
21
The Orbitals for N2
22
A Set of dsp3 Hybrid Orbitals on a Phosphorus Atom
23
An Octahedral Set of d2sp3 Orbitals on a Sulfur
Atom
24
The Relationship of the Number of Effective
Pairs, Their Spatial Arrangement, and the Hybrid
Orbital Set Required
25
The Localized Electron Model
  • Three Steps
  • Draw the Lewis structure(s)
  • Determine the arrangement of electron pairs
    (VSEPR model).
  • Specify the necessary hybrid orbitals.

26
Molecular Orbitals (MO)
  • Analagous to atomic orbitals for atoms, MOs are
    the quantum mechanical solutions to the
    organization of valence electrons in molecules.
  • Molecular orbitals have many of the same
    characteristics as atomic orbitals, such as they
    can hold two electrons with opposite spins and
    the square of the molecular orbital wave function
    indicates electron probability.

27
The Combination of Hydrogen 1s Atomic Orbitals
to Form Molecular Orbitals
28
The Molecular Orbitals for H2
29
Types of MOs
  • bonding lower in energy than the atomic
    orbitals from which it is composed. Electrons in
    this type of orbital will favor the molecule.
  • antibonding higher in energy than the atomic
    orbitals from which it is composed. Electrons in
    this type of orbital will favor the separated
    atoms.

30
Bonding and Antibonding Molecular Orbitals (MOs)
31
The Molecular Orbital Energy-Level Diagram for
the H2 Molecule
32
The Molecular Orbital Energy-Level Diagram for
the H2- Ion
33
Bond Order (BO)
  • Difference between the number of bonding
    electrons and number of antibonding electrons
    divided by two.
  • Bonds order is an indication of bond strength.
    Large bond order means greater bond strength.

34
The Molecular Orbital Energy-Level Diagram for
the He2 Molecule
35
Bonding in Homonuclear Diatomic Molecules
  • In order to participate in MOs, atomic orbitals
    must overlap in space. (Therefore, only valence
    orbitals of atoms contribute significantly to
    MOs.)

36
The Relative Sizes of the Lithium 1s and 2s
Atomic Orbitals
37
The Molecular Orbital Energy-Level Diagram for
the Li2 Molecule
38
The Molecular Orbitals from p Atomic Orbitals
39
The Expected Molecular Orbital Energy-Level
Diagram Resulting from the Combination of the 2p
Orbitals on Two Boron Atoms
40
The Expected Molecular Orbital Energy-Level
Diagram for the B2 Molecule
41
Paramagnetism
  • unpaired electrons
  • attracted to induced magnetic field
  • much stronger than diamagnetism

42
Diamagnetism
  • paired electrons
  • repelled from induced magnetic field
  • much weaker than paramagnetism

43
Diagram of the Kind of Apparatus Used to Measure
the Paramagnetism of a Sample
44
The Correct Molecular Orbital Energy-Level
Diagram for the B2 Molecule
45
Molecular Orbital Summary of Second Row Diatomics
46
Outcomes of MO Model
  • As bond order increases, bond energy increases
    and bond length decreases.
  • Bond order is not absolutely associated with
  • a particular bond energy.
  • N2 has a triple bond, and a correspondingly
  • high bond energy.
  • O2 is paramagnetic. This is predicted by the MO
    model, not by the LE model, which predicts
    diamagnetism.

47
Combining LE and MO Models
  • ? bonds can be described as being localized.
  • ? bonding must be treated as being delocalized.

48
The Resonance Structures for O3 and NO3-
49
A Benzene Ring
50
The Sigma System for Benzene
51
The Pi System for Benzene
52
The NO3- Ion
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