1. End Show © Copyright Pearson Prentice Hall Slide 1 of 33 Polar Bonds and Molecules Snow covers approximately 23 percent of Earth’s surface. Each individual snowflake is formed from as many as 100 snow crystals. The polar bonds in water molecules influence the distinctive geometry of snowflakes. 8.4

2. End Show © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Slide 2 of 33 8.4 Bond Polarity How do electronegativity values determine the charge distribution in a polar bond?

3. End Show Slide 3 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Bond Polarity When the atoms in a bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally, and the bond is a nonpolar covalent bond.

4. End Show Slide 4 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Bond Polarity The bonding pairs of electrons in covalent bonds are pulled by the nuclei.

5. End Show Slide 5 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Bond Polarity The chlorine atom attracts the electron cloud more than the hydrogen atom does.

6. End Show Slide 6 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Bond Polarity A polar covalent bond, known also as a polar bond, is a covalent bond between atoms in which the electrons are shared unequally. The more electronegative atom attracts electrons more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.

7. End Show Slide 7 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Bond Polarity 8.4 Notes from WB: as the difference in electronegativity between the atoms in the bond increases the ionic character of the bond increases and the covalent character decreases. Ionic bonds are generally formed between metals and nonmetals. WB gives the range for ionic bonds to be a difference of greater than or equal to 1.7 but you will need to consider the type of elements as well as the electronegativity values. HF, for example, has a polar covalent bond (not an ionic bond).

8. End Show © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Slide 8 of 33 Polar Molecules What happens to polar molecules between a pair of oppositely charged metal plates? 8.4

9. End Show Slide 9 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Polar Molecules In a polar molecule, one end of the molecule is slightly negative and the other end is slightly positive. A molecule that has two poles is called a dipolar molecule, or dipole. 8.4

10. End Show © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Slide 10 of 33 Polar Molecules When polar molecules are placed between oppositely charged plates, they tend to become oriented with respect to the positive and negative plates. 8.4

11. End Show Slide 11 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Polar Molecules A hydrogen chloride molecule is a dipole. 8.4

12. End Show © Copyright Pearson Prentice Hall Slide 12 of 33 Polar Bonds and Molecules > Polar Molecules Animation 10 Learn to distinguish between polar and nonpolar molecules.

13. End Show © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Slide 13 of 33 8.4 Attractions Between Molecules How do intermolecular attractions compare with ionic and covalent bonds?

14. End Show Slide 14 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Attractions Between Molecules Intermolecular attractions are weaker than either ionic or covalent bonds. These attractions are responsible for determining whether a molecular compound is a gas, a liquid, or a solid at a given temperature.

15. End Show Slide 15 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 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 (1837–1923). 8.4

16. End Show Slide 16 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Attractions Between Molecules Dipole interactions occur when polar molecules are attracted to one another. 8.4

17. End Show Slide 17 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Attractions Between Molecules Dispersion forces, the weakest of all molecular interactions, are caused by the motion of electrons. The strength of dispersion forces generally increases as the number of electrons in a molecule increases.

18. End Show Slide 18 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > What are van der waals forces? http://antoine.frostburg.edu/chem/senese/101 /liquids/faq/h-bonding-vs-london-forces.shtml Hydrogen bonding video: http://www.youtube.com/watch?v=LGwyB euVjhU

19. End Show Slide 19 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 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. 8.4

20. End Show Slide 20 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Attractions Between Molecules Hydrogen Bonding in Water

21. End Show Slide 21 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Attractions Between Molecules The relatively strong attractive forces between water molecules cause the water to form small drops on a waxy surface. 8.4

22. End Show © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Slide 22 of 33 Intermolecular Attractions and Molecular Properties Why do network solids have high melting points? 8.4

23. End Show Slide 23 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Intermolecular Attractions and Molecular Properties Network solids (or network crystals) are solids in which all of the atoms are covalently bonded to each other. Network solids consist of molecules that do not melt until the temperature reaches 1000°C or higher, or they decompose without melting at all.

24. End Show © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Slide 24 of 33 Intermolecular Properties and Molecular Properties Melting a network solid would require breaking covalent bonds throughout the solid. 8.4

25. End Show Slide 25 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Intermolecular Attractions and Molecular Properties Diamond is an example of a network solid. Diamond does not melt. It vaporizes to a gas at 3500°C or above.

26. End Show Slide 26 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > 8.4 Intermolecular Attractions and Molecular Properties Silicon Carbide is a network solid. It has a melting point of about 2700°C.

27. End Show © Copyright Pearson Prentice Hall Slide 27 of 33 Polar Bonds and Molecules > Intermolecular Attractions and Molecular Properties Simulation 8 Relate melting and boiling points to the strength of intermolecular forces.

28. End Show Slide 28 of 33 © Copyright Pearson Prentice Hall Polar Bonds and Molecules > Intermolecular Attractions and Molecular Properties 8.4

29. End Show © Copyright Pearson Prentice Hall Slide 29 of 33 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 8.4 Section Quiz. 8.4.

30. © Copyright Pearson Prentice Hall Slide 30 of 33 End Show 8.4 Section Quiz. 1.In a molecule, the atom with the largest electronegativity value a.repels electrons more strongly and aquires a slightly negative charge. b.repels electrons more strongly and aquires a slightly positive charge. c.attracts electrons more strongly and aquires a slightly positive charge. d.attracts electrons more strongly and aquires a slightly negative charge.

31. © Copyright Pearson Prentice Hall Slide 31 of 33 End Show 2. When polar molecules are placed between oppositely charged plates, the negative a.molecules stick to the positive plates. b.molecules stick to the negative plates. c.ends of the molecules turn toward the positive plates. d.ends of the molecules turn toward the negative plates. 8.4 Section Quiz.

32. © Copyright Pearson Prentice Hall Slide 32 of 33 End Show 3. Which of the following bond types is the weakest? a.ionic bond b.Van der Waals force c.covalent bond d.hydrogen bond 8.4 Section Quiz.