MolecularGeometryandChemicalBondingTheory章分子结构和化学键理论
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Four electron pairs are 109.5° apart in three dimensions (a tetrahedral arrangment).
10 | 14
Five electron pairs are arranged with three pairs in a plane 120° apart and two pairs at 90°to the plane and 180° to each other (a trigonal bipyramidal arrangement).
10 | 7
4. Description of Multiple Bonding
a. Define an s (sigma) bond. b. Define a p (pi) bond.
c. Apply valence bond theory (multiple bonding).
d. Explain geometric, or cis-trans, isomers in
10 | 3
Learning Objectives
Molecular Geometry and Directional Bonding 1. The Valence-Shell Electron-Pair Repulsion
(VSEPR) Model a. Define molecular geometry. b. Define valence-shell electron-pair repulsion
Six electron pairs are 90° apart (an octahedral arrangement).
This is illustrated on the next slide.
10 | 15
10 | 16
These arrangements are illustrated below with balloons and models of molecules for each.
10 | 6
3. Valence Bond Theory a. Define valence bond theory. b. State the two conditions needed for bond formation according to valence bond theory. c. Define hybrid orbitals. d. State the five steps in describing bonding, following the valence bond theory. e. Apply valence bond theory to a molecule with two, three, or four electron pairs. f. Apply valence bond theory to a molecule with five or six electron pairs.
7. Molecular Orbitals and Delocalized Bonding a. Describe the delocalized bonding in molecules such as O3.
10 | 10
In this chapter, we discuss how to explain the geometries of molecules in terms of their electronic structures. We also explore two theories of chemical bonding: valence bond theory and molecular orbital theory.
The diagram on the next slide illustrates this.
10 | 13
Two electron pairs are 180° apart ( a linear arrangement).
Three electron pairs are 120° apart in one plane (a trigonal planar arrangement).
10 | 2
Molecular Orbital Theory Although valence bond theory satisfactorily describes most molecules, it has trouble explaining the bonding in molecules such as oxygen, O2, which has even numbers of electrons but is paramagnetic. Molecular orbital theory is an alternative theory that views the electronic structure of molecules much the way we think of atoms—in terms of orbitals that are successively occupied by electrons.
10 | 17
terms of the p-bond description of a double
bond.
10 | 8
Molecular Orbital Theory 5. Principles of Molecular Orbital Theory
a. Define molecular orbital theory. b. Define bonding orbitals and antibonding
5. Principles of Molecular Orbital Theory 6. Electron Configurations of Diatomic Molecules of the
Second-Period Elements 7. Molecular Orbitals and Delocalized Bonding
g. Predict the molecular geometry for a molecule with five or six electron pairs.
10 | 5
2. Dipole Moment and Molecular Geometry a. Define dipole moment. b. Explain the relationship between the dipole moment and molecular geometry. c. Note that the polarity of a molecule can affect certain properties, such as boiling point.
model. c. Note the difference between the
arrangement of electron pairs about a central atom and molecular geometry.
10 | 4
d. Note the four steps in the prediction of geometry by the VSEPR model.
1. The Valence-Shell Electron-Pair Repulsion (VSEPR) Model 2. Dipole Moment and Molecular Geometry 3. Valence Bond Theory 4. Description of Multiple Bonding
10 | 11
Molecular geometry is the general shape of a molecule, as determined by the relative positions of the atomic nuclei.
10 | 12
The valence-shell electron-pair repulsion (VSEPR) model predicts the shapes of molecules and ions by assuming that the valence-shell electron pairs are arranged about each atom so that electron pairs are kept as far away from one another as possible, thereby minimizing electron pair repulsions.
10 Biblioteka Baidu 9
6. Electron Configurations of Diatomic Molecules of the Second-Period Elements a. Define homonuclear diatomic molecules and heteronuclear diatomic molecules. b. Describe molecular orbital configurations (homonuclear diatomic molecules). c. Describe molecular orbital configurations (heteronuclear diatomic molecules).
e. Predict the molecular geometry for a molecule with two, three, or four electron pairs.
f. Note that a lone pair tends to require more space than a corresponding bonding pair and that a multiple bond requires more space than a single bond.
Chapter 10 Molecular Geometry
and Chemical Bonding Theory
10 | 1
Contents and Concepts
Molecular Geometry and Directional Bonding We can predict the molecular geometry of a molecule—that is, its general shape as determined by the relative positions of atomic nuclei—with a simple model: the valence-shell electron-pair repulsion model. After exploring molecular geometry, we explain chemical bonding by means of valence bond theory, which gives us insights into why bonds form and why they have definite directions in space, giving particular molecular geometries.
orbitals. c. Define bond order. d. State the two factors that determine the
strength of interaction between two atomic orbitals. e. Describe the electron configurations of H2, He2, Li2, and Be2.
10 | 14
Five electron pairs are arranged with three pairs in a plane 120° apart and two pairs at 90°to the plane and 180° to each other (a trigonal bipyramidal arrangement).
10 | 7
4. Description of Multiple Bonding
a. Define an s (sigma) bond. b. Define a p (pi) bond.
c. Apply valence bond theory (multiple bonding).
d. Explain geometric, or cis-trans, isomers in
10 | 3
Learning Objectives
Molecular Geometry and Directional Bonding 1. The Valence-Shell Electron-Pair Repulsion
(VSEPR) Model a. Define molecular geometry. b. Define valence-shell electron-pair repulsion
Six electron pairs are 90° apart (an octahedral arrangement).
This is illustrated on the next slide.
10 | 15
10 | 16
These arrangements are illustrated below with balloons and models of molecules for each.
10 | 6
3. Valence Bond Theory a. Define valence bond theory. b. State the two conditions needed for bond formation according to valence bond theory. c. Define hybrid orbitals. d. State the five steps in describing bonding, following the valence bond theory. e. Apply valence bond theory to a molecule with two, three, or four electron pairs. f. Apply valence bond theory to a molecule with five or six electron pairs.
7. Molecular Orbitals and Delocalized Bonding a. Describe the delocalized bonding in molecules such as O3.
10 | 10
In this chapter, we discuss how to explain the geometries of molecules in terms of their electronic structures. We also explore two theories of chemical bonding: valence bond theory and molecular orbital theory.
The diagram on the next slide illustrates this.
10 | 13
Two electron pairs are 180° apart ( a linear arrangement).
Three electron pairs are 120° apart in one plane (a trigonal planar arrangement).
10 | 2
Molecular Orbital Theory Although valence bond theory satisfactorily describes most molecules, it has trouble explaining the bonding in molecules such as oxygen, O2, which has even numbers of electrons but is paramagnetic. Molecular orbital theory is an alternative theory that views the electronic structure of molecules much the way we think of atoms—in terms of orbitals that are successively occupied by electrons.
10 | 17
terms of the p-bond description of a double
bond.
10 | 8
Molecular Orbital Theory 5. Principles of Molecular Orbital Theory
a. Define molecular orbital theory. b. Define bonding orbitals and antibonding
5. Principles of Molecular Orbital Theory 6. Electron Configurations of Diatomic Molecules of the
Second-Period Elements 7. Molecular Orbitals and Delocalized Bonding
g. Predict the molecular geometry for a molecule with five or six electron pairs.
10 | 5
2. Dipole Moment and Molecular Geometry a. Define dipole moment. b. Explain the relationship between the dipole moment and molecular geometry. c. Note that the polarity of a molecule can affect certain properties, such as boiling point.
model. c. Note the difference between the
arrangement of electron pairs about a central atom and molecular geometry.
10 | 4
d. Note the four steps in the prediction of geometry by the VSEPR model.
1. The Valence-Shell Electron-Pair Repulsion (VSEPR) Model 2. Dipole Moment and Molecular Geometry 3. Valence Bond Theory 4. Description of Multiple Bonding
10 | 11
Molecular geometry is the general shape of a molecule, as determined by the relative positions of the atomic nuclei.
10 | 12
The valence-shell electron-pair repulsion (VSEPR) model predicts the shapes of molecules and ions by assuming that the valence-shell electron pairs are arranged about each atom so that electron pairs are kept as far away from one another as possible, thereby minimizing electron pair repulsions.
10 Biblioteka Baidu 9
6. Electron Configurations of Diatomic Molecules of the Second-Period Elements a. Define homonuclear diatomic molecules and heteronuclear diatomic molecules. b. Describe molecular orbital configurations (homonuclear diatomic molecules). c. Describe molecular orbital configurations (heteronuclear diatomic molecules).
e. Predict the molecular geometry for a molecule with two, three, or four electron pairs.
f. Note that a lone pair tends to require more space than a corresponding bonding pair and that a multiple bond requires more space than a single bond.
Chapter 10 Molecular Geometry
and Chemical Bonding Theory
10 | 1
Contents and Concepts
Molecular Geometry and Directional Bonding We can predict the molecular geometry of a molecule—that is, its general shape as determined by the relative positions of atomic nuclei—with a simple model: the valence-shell electron-pair repulsion model. After exploring molecular geometry, we explain chemical bonding by means of valence bond theory, which gives us insights into why bonds form and why they have definite directions in space, giving particular molecular geometries.
orbitals. c. Define bond order. d. State the two factors that determine the
strength of interaction between two atomic orbitals. e. Describe the electron configurations of H2, He2, Li2, and Be2.