Smells Unit

1. Smells Unit Investigation IV: Molecules in Action Lesson 1: Breaking Up Is Hard to Do?? Lesson 2: How Does the Nose Know? Lesson 3: Attractive Molecules Lesson 4: Polar Bears and Penguins Lesson 5: Thinking (Electro)Negatively Lesson 6: I Can Relate Lesson 7: Sniffing It Out . . . Lesson 8: Take a Deep Breath

2. Smells Unit – Investigation IV Lesson 1: Breaking Up Is Hard to Do??

3. ChemCatalyst • Which drawing best represents what you think is going on with the molecules in the smell vials? Explain your reasoning. (Pay attention to the key.) Key Molecules C, H, and O atoms Unit 2 • Investigation IV

4. The Big Question • Do molecules break apart into atoms when they escape from the smell vial or do they stay together as molecules? Unit 2 • Investigation IV

5. You will be able to: • Explain smelling in the context of phase change. Unit 2 • Investigation IV

6. Vial H ethyl acetate sweet Vial G butyric acid putrid Notes C4H8O2 Unit 2 • Investigation IV

7. Activity • Purpose: Your goal in this activity is to determine which picture; 1, 2, 3, or 4, is the best representation of what is going on with the molecules in Smell Vials G and H. Key Molecules C, H, and O atoms (cont.) Unit 2 • Investigation IV

8. (cont.) Unit 2 • Investigation IV

9. Making Sense • Based on this activity, do you think the substances that you smell are staying together as intact molecules or breaking apart into individual atoms? Explain your thinking. Unit 2 • Investigation IV

10. Notes • Any time a substance goes from one state of matter (solid, liquid or gas) to another state of matter, it is called a phase change. • Molecules are stable when they remain together even when undergoing a phase change. Unit 2 • Investigation IV

11. Check-In • Examine the following drawing and pick the best explanation from the two below. Unit 2 • Investigation IV

12. Wrap-Up • The idea that molecules remain together as units explains why molecules with the same molecular formula can have different properties such as smell. • Molecules undergoing a phase change do not break apart. • Molecules are collections of atoms that satisfy the octet rule; as such they are very stable. Unit 2 • Investigation IV

13. Smells Unit – Investigation IV Lesson 2: How Does the Nose Know?

14. ChemCatalyst • How do you think your nose detects a smell? Unit 2 • Investigation IV

15. The Big Question • How does our nose detect different smells? Unit 2 • Investigation IV

16. You will be able to: • Understand how a molecule is detected by the nose. Unit 2 • Investigation IV

17. Activity • Purpose: To design a model that explains how molecules are detected in the nose. Unit 2 • Investigation IV

18. Making Sense • No Making Sense question. Unit 2 • Investigation IV

19. Notes • A receptor site is a tiny physiological structure made up of large, complex protein molecules that fold to form a specific shape. Molecules with matching shapes fit inside these structures. When molecules attach to receptor sites they stimulate nerves to send a signal to the brain. Unit 2 • Investigation IV

20. Check-In • One of the molecules that makes coffee smell is 2-furylmethanethiol: • Write down everything you know about how this molecule is detected by the nose. • Draw a possible receptor site for this molecule. Unit 2 • Investigation IV

21. Wrap-Up • The currently accepted model for smell describes smell molecules landing in receptor sites that fit or "receive" the shape of the smell molecules. • In the receptor site model each receptor site has a specific shape, which corresponds to the shape of just a few smell molecules. Unit 2 • Investigation IV

22. Smells Unit – Investigation IV Lesson 3: Attractive Molecules

23. ChemCatalyst • If a molecule fits into a receptor site in the nose, it seems as if it should smell. Yet most of the molecules that make up the air do not have a smell. What do you think is going on? Doesn’t smell? Smells Smells Here are some of the gases in air: O2 (oxygen), N2 (nitrogen), CO2 (carbon dioxide), Ar (argon). Unit 2 • Investigation IV

24. The Big Question • In what ways do molecules interact with each other? Unit 2 • Investigation IV

25. You will be able to: • Describe a polar molecule. Unit 2 • Investigation IV

26. Activity • Purpose: In this lesson, you observe the response of certain liquids to a charged wand and the behavior of the same liquids as droplets. These activities give you information about possible interactions between molecules. This is a three-part activity. (cont.) Unit 2 • Investigation IV

27. (cont.) (cont.) Unit 2 • Investigation IV

28. (cont.) Unit 2 • Investigation IV

29. Making Sense • If water molecules are carrying a partial charge, as shown in the following picture, how do you think a group of water molecules would behave towards each other? Draw a picture of several water molecules interacting, to illustrate your thinking. Unit 2 • Investigation IV

30. Notes • Some molecules have a slight charge on opposite ends of the molecule. Molecules that have partial charges are called polar molecules. One end of the molecule has a partial negative charge and the other end of the molecule has a partial positive charge. Unit 2 • Investigation IV

31. Notes • The charged wand shows us that the molecules in certain liquids (polar liquids) orient themselves in response to an electrostatic charge in their vicinity. This causes the liquid to move in the direction of the charge. (cont.) Unit 2 • Investigation IV

32. Notes (cont.) • Hexane was not attracted to the charged wand. So it would seem reasonable to suggest that different ends of the molecule do not have opposite partial charges. Molecules such as this are called nonpolar molecules. (cont.) Unit 2 • Investigation IV

33. Notes (cont.) • The attraction that happens between individual polar molecules is called an intermolecular interaction or an intermolecular attraction. Unit 2 • Investigation IV

34. Check-In • Acetone is polar. Name two other things that are probably true about acetone. Unit 2 • Investigation IV

35. Wrap-Up • Polar molecules have partial charges on parts of the molecule. • Polar molecules are attracted to a charge. • Polar molecules are attracted to each other. These intermolecular interactions account for many observable properties. Unit 2 • Investigation IV

36. Smells Unit – Investigation IV Lesson 4: Polar Bears and Penguins

37. ChemCatalyst • Consider the following illustration: (cont.) Unit 2 • Investigation IV

38. (cont.) • Draw the Lewis dot structure for HCl. • If the penguin represents a hydrogen atom and the polar bear represents a chlorine atom, what does the ice cream represent in the drawing? What do you think the picture is trying to illustrate? • Would HCl be attracted to the charge wand? Explain your thinking. Unit 2 • Investigation IV

39. The Big Question • How can we explain partial charges on molecules? Unit 2 • Investigation IV

40. You will be able to: • Recognize and explain a polar bond. Unit 2 • Investigation IV

41. Activity • Purpose: In this lesson you will be exploring polarity and bonding between atoms in greater detail. A comic book will provide new information about these topics and will introduce you to the concept of electronegativity, which helps us to understand partial charges. Unit 2 • Investigation IV

42. Making Sense • What does electronegativity have to do with polarity? Unit 2 • Investigation IV

43. Notes • This tendency of an atom to attract electrons shared between two atoms is called electronegativity. • An atom that strongly attracts the shared electrons is considered highly electronegative. The atom with lower electronegativity will end up with a partial positive charge on it. The result is a polar bond. Unit 2 • Investigation IV

44. Notes (cont.) • Chemists have a specific name for a molecule that has two poles—it is called a dipole. ("Di" means two.) (cont.) Unit 2 • Investigation IV

45.   Notes (cont.) • This illustration also uses a crossed arrow to show the direction of the dipole in HCl. The crossed end of the arrow indicates the positive (+) end of the polar bond and the arrow points in the direction of the negative (-) end. Unit 2 • Investigation IV

46. Notes (cont.) • Polar molecules are also called dipoles. The prefix di- means two. A dipole is a molecule with two partially charged ends, or poles. Chemists refer to polar molecules as dipoles and they also say that molecules with polar bonds have dipoles. This nomenclature can be a bit confusing with two related meanings for two closely-related meanings for the same word. Unit 2 • Investigation IV

47. Notes (cont.) • Nonpolar covalent bonds are the only bonds in which the electrons are truly shared equally. • If the electronegativities between two atoms are even slightly different, they form what is called a polar covalent bond. • When the electronegativities between two atoms are greatly different, the bond is called an ionic bond. In the case of an ionic bond the electron of one atom is completely given up to the other atom. Unit 2 • Investigation IV

48. Notes (cont.) Unit 2 • Investigation IV

49. Check-In • Is the bond between these atoms polar? Explain your reasoning. • How would the atoms be portrayed in the comic book—as polar bears, penguins, or both? Explain. Unit 2 • Investigation IV

50. Wrap-Up • Anytime there are two different types of atoms sharing electrons, there will be a partial negative charge on one atom and a partial positive charge on the other atom. • Electronegativity measures the tendency of an atom to attract the electrons in a bond. (cont.) Unit 2 • Investigation IV