1. Chapter 8 Covalent Bonding 8.4 Polar Bonds and Molecules
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. Draw a LEWIS Dot structure for H20
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3. Polar Covalent, Non-Polar, Ionic?
Bond Polarity
Polar Covalent, Non-Polar, Ionic?
Oxygen has an electronegativity of 3.5
Hydrogen has an electronegativity of 2.1
Is Water Polar, Non-Polar, or Ionic?
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4. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
The O—H bonds in a water molecule are polar.
The highly electronegative oxygen partially pulls the bonding electrons away from hydrogen.
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5. Attractions Between Molecules
Molecules can be attracted to each other by a variety of different forces.
Intermolecular attractions are weaker than either ionic or covalent bonds.
Among other things, these attractions are responsible for determining whether a molecular compound is a gas, a liquid, or a solid at a given temperature.
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6. Attractions Between Molecules
Van der Waals Forces
The two weakest attractions between molecules are collectively called van der Waals forces, named after the Dutch chemist Johannes van der Waals.
Van der Waals forces consist of dipole interactions and dispersion forces.
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7. Attractions Between Molecules
Van der Waals Forces
Dipole interactions occur when polar molecules are attracted to one another.
The electrical attraction occurs between the oppositely charged regions of polar molecules.
Dipole interactions are similar to, but much weaker than, ionic bonds.
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8. Attractions Between Molecules
Dipole Forces
The slightly negative region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule.
Dipole interactions are similar to, but much weaker than, ionic bonds.
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9. Attractions Between Molecules
Van der Waals Forces
Dispersion forces, the weakest of all molecular interactions, are caused by the motion of electrons.
When the moving electrons happen to be momentarily more on the side of a molecule closest to a neighboring molecule, their electric force influences the neighboring molecule’s electrons to be momentarily more on the opposite side.
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10. Attractions Between Molecules
Hydrogen Bonds
The dipole interactions in water produce an attraction between water molecules.
Each O—H bond in the water molecule is highly polar, and the oxygen acquires a slightly negative charge because of its greater electronegativity.
The hydrogens in water molecules acquire a slightly positive charge.
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11. Attractions Between Molecules
Hydrogen Bonds
The positive region of one water molecule attracts the negative region of another water molecule.
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12. Attractions Between Molecules
Hydrogen Bonds
This relatively strong attraction, which is also found in hydrogen-containing molecules other than water, is called a hydrogen bond.
Hydrogen bond
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13. Attractions Between Molecules
Hydrogen Bonds
Hydrogen bonds are attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom.
Hydrogen bonding always involves hydrogen.
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14. Attractions Between Molecules
Hydrogen Bonds
A hydrogen bond has about 5 percent of the strength of the average covalent bond.
Hydrogen bonds are the strongest of the intermolecular forces.
They are extremely important in determining the properties of water and biological molecules, like proteins.
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15. Glossary Terms
dipole: a molecule that has two poles, or regions with opposite charges
van der Waals forces: the two weakest intermolecular attractions—dispersion interactions and dipole forces
dipole interactions: intermolecular forces resulting from the attraction of oppositely charged regions of polar molecules
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16. Glossary Terms
dispersion forces: attractions between molecules caused by the electron motion on one molecule affecting the electron motion on the other through electrical forces; these are the weakest interactions between molecules
hydrogen bonds: attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom
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