1. Chapter 8 Covalent Bonding 8.3 Bonding Theories
8.1 Molecular Compounds
8.2 The Nature of Covalent Bonding
8.3 Bonding Theories
8.4 Polar Bonds and Molecules
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2. (electron dot structure)
VSEPR Theory
Electron dot structures fail to reflect the three-dimensional shapes of molecules.
The electron dot structure and structural formula of methane (CH4) show the molecule as if it were flat and merely two-dimensional.
Methane
(electron dot structure)
(structural formula)
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3. In reality, methane molecules are three-dimensional.
VSEPR Theory
In reality, methane molecules are three-dimensional.
The hydrogens in a methane molecule are at the four corners of a geometric solid called a regular tetrahedron.
In this arrangement, all of the H–C–H angles are 109.5°, the tetrahedral angle.
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4. VSEPR Theory
In order to explain the three-dimensional shape of molecules, scientists use valence-shell electron-pair repulsion theory (VSEPR theory).
VSEPR theory states that the repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.
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5. However, one of the valence-electron pairs is an unshared pair.
VSEPR Theory
Unshared pairs of electrons are also important in predicting the shapes of molecules.
The nitrogen in ammonia (NH3) is surrounded by four pairs of valence electrons.
However, one of the valence-electron pairs is an unshared pair.
Ammonia (NH3)
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6. Here are some common molecular shapes.
VSEPR Theory
Here are some common molecular shapes.
Linear
Trigonal planar
Bent
Pyramidal
Tetrahedral
Trigonal
bipyramidal
Octahedral
Square
planar
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7. Animated molecular geometries http://intro. chem. okstate
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8. VSEPR Theory
Go online to find THREE examples of molecules that represent the 8 molecular shapes. Make a display of your product. Molecular geometry
Linear
Trigonal planar
Bent
Pyramidal
Tetrahedral
Trigonal
bipyramidal
Octahedral
Square
planar
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9. example
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10. Grading Rubric
Task points Student collected 24 points 3 examples for each Shape Students drew and 24 point Labelled each example Quality of work: excellent 6 points good 4 points careless 0 points
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11. Hybrid Orbitals
The VSEPR theory works well when accounting for molecular shapes, but it does not help much in describing the types of bonds formed.
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12. Hybrid Orbitals
Orbital hybridization provides information about both molecular bonding and molecular shape.
In hybridization, several atomic orbitals mix to form the same total number of equivalent hybrid orbitals.
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13. Key Concepts
Just as an atomic orbital belongs to a particular atom, a molecular orbital belongs to a molecule as a whole.
In order to explain the three-dimensional shape of molecules, scientists use the valence-shell electron-pair repulsion theory (VSEPR theory).
Orbital hybridization provides information about both molecular bonding and molecular shape.
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14. molecular orbital: an orbital that applies to the entire molecule
Glossary Terms
molecular orbital: an orbital that applies to the entire molecule
bonding orbital: a molecular orbital that can be occupied by two electrons of a covalent bond
sigma bond ( bond): a bond formed when two atomic orbitals combine to form a molecular orbital that is symmetrical around the axis connecting the two atomic nuclei
pi bond ( bond): a covalent bond in which the bonding electrons are most likely to be found in sausage-shaped regions above and below the bond axis of the bonded atoms
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15. Glossary Terms
tetrahedral angle: a bond angle of 109.5° that results when a central atom forms four bonds directed toward the center of a regular tetrahedron
VSEPR theory: valence-shell electron-pair repulsion theory; because electron pairs repel, molecules adjust their shapes so that valence electron pairs are as far apart as possible
hybridization: the mixing of several atomic orbitals to form the same total number of equivalent hybrid orbitals
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