Investigation IV: Molecules in Action 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

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

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

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

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

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

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

Does the picture show why G and H smell different? (cont.) Picture Does the picture show why G and H smell different? Does the picture show why G and H have different properties as liquids? Either support or criticize this picture as a good representation for what happens in the smell vials. 1 2 3 4 Unit 2 • Investigation IV

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

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

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

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

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

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

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

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

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

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

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

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

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

Smells Unit – Investigation IV Lesson 3: Attractive Molecules

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

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

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

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

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

Results of charged wand test (cont.) Molecule Results of charged wand test water attracted isopropanol acetic acid hexane Unit 2 • Investigation IV

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

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

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

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

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

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

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

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

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

Draw the Lewis dot structure for HCl. (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

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

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

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

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

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

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

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

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

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

Notes (cont.) Unit 2 • Investigation IV

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

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

(cont.) The bonds are labeled nonpolar covalent, polar covalent, and ionic as the difference in electronegativity between the two atoms in the bond increases. Unit 2 • Investigation IV

Smells Unit – Investigation IV Lesson 5: Thinking (Electro)Negatively

ChemCatalyst Explain how the illustration and the table might relate to each other. Unit 2 • Investigation IV

The Big Question How does electronegativity relate to polarity and bonding? Unit 2 • Investigation IV

You will be able to: Determine whether a bond is polar, nonpolar, or ionic. Unit 2 • Investigation IV

Activity Purpose: This lesson explores electronegativity in a quantitative fashion—that is, it applies numbers to our investigation of polarity. Using the electronegativity scale it is possible to compare atoms and find out which ones will attract electrons more strongly in a bond. (cont.) Unit 2 • Investigation IV

(cont.) Unit 2 • Investigation IV

Making Sense Explain how you would determine both the direction and degree of polarity of a bond between two different atoms using the electronegativity scale. (cont.) Unit 2 • Investigation IV

(cont.) Unit 2 • Investigation IV

Notes A molecule made from only two atoms is called a diatomic molecule. (cont.) Unit 2 • Investigation IV

Notes (cont.) Nonpolar covalent bonds are really the only true covalent bonds. If the electronegativities between two atoms are even slightly different they form what is called a polar covalent bond. In polar covalent bonds the bonding electrons are located closer to the more electronegative atom. (cont.) Unit 2 • Investigation IV

Notes (cont.) 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

Check-In To what degree do the K and Cl atoms in KCl, potassium chloride, share electrons? Is the bond in potassium chloride nonpolar, polar, or ionic? Explain your thinking. Unit 2 • Investigation IV

Wrap-Up Electronegativity measures how strongly an atom will attract shared electrons. The greater the difference in electronegativity between two atoms, the more polar the bond will be. In the case of an ionic bond, the electronegativities between two atoms are so greatly different that the electron(s) of one atom is(are) completely given up to the other atom. Unit 2 • Investigation IV

Smells Unit – Investigation IV Lesson 6: I Can Relate

ChemCatalyst HCl (hydrogen chloride) and NH3 (ammonia) smell and they dissolve easily in water. O2, N2, and CH4 (oxygen, nitrogen, and methane) do not smell and they do not dissolve easily in water. How can you explain these differences? Unit 2 • Investigation IV

The Big Question How does polarity help to explain what is happening between smell molecules and the nose? Unit 2 • Investigation IV

You will be able to: Use polarity to predict whether a molecule will have a smell. Unit 2 • Investigation IV

Notes Water molecules in liquid water orient so that the H atom from one water molecule is pointed toward the O atom of another water molecule. This type of interaction with an H atom between two electronegative atoms on two different molecules is called a hydrogen bond. Unit 2 • Investigation IV

Activity Purpose: The goal of this lesson is to give you practice in determining the polarity of small molecules with more than two atoms. In addition, you will explore how polarity and electronegativity relate back to smell. (cont.) Unit 2 • Investigation IV

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

(cont.) (cont.) HCl NH3 H2S CF4 CH2O CClF3 CH4O Unit 2 • Investigation IV

(cont.) Molecule Has a smell? N2 No NH3 Yes PH3 HBr CH4 CO2 H2Se AsH3 Unit 2 • Investigation IV

Making Sense Explain why polarity might be an important concept to understand when trying to figure out the chemistry of smell. Unit 2 • Investigation IV

Notes (cont.) Unit 2 • Investigation IV

Notes (cont.) Nonpolar molecules (cont.) Unit 2 • Investigation IV

Notes (cont.) Polar molecules (cont.) Unit 2 • Investigation IV

Notes (cont.) Polar molecules tend to dissolve more easily in other polar molecules because of the intermolecular forces between the molecules. Nonpolar molecules tend not to dissolve in polar substances. Unit 2 • Investigation IV

Check-In Due to differences in electronegativity, we expect HCN, hydrogen cyanide, to be polar. Since water is polar as well, which way do you think water and hydrogen cyanide molecules would orient with each other? Explain your reasoning. (cont.) Unit 2 • Investigation IV

Do you think HCN will have a smell? Explain. (cont.) Do you think HCN will have a smell? Explain. Unit 2 • Investigation IV

Wrap-Up Differences in electronegativity values can be used to determine the direction of the dipole for an entire molecule. The polarity or nonpolarity of a molecule is responsible for a great many of its observable properties. Small polar molecules smell. Small nonpolar molecules do not smell. Unit 2 • Investigation IV

Smells Unit – Investigation IV Lesson 7: Sniffing It Out . . .

ChemCatalyst If you place an open perfume bottle and a piece of paper in a sunny window, the aroma of the perfume will soon fill the air, but you won’t smell the paper at all. Explain what is going on. What is the heat from the sun doing to the perfume to increase its smell? Unit 2 • Investigation IV

The Big Question How can we apply what we’ve learned about smell to our daily lives? Unit 2 • Investigation IV

You will be able to: Describe the physical and chemical factors that determine whether on not a type of molecule will smell. Unit 2 • Investigation IV

Activity Purpose: This lesson wraps up the Smells Unit by introducing data showing that size of molecules, type of bonding, and phase, together with polarity all determine if a substance will have a smell. (cont.) Unit 2 • Investigation IV

(cont.) (cont.) Substance type Examples Smell? Phase Bonding Size Name Formula Molecular Nonpolar covalent Small molecules nitrogen oxygen carbon dioxide methane N2 O2 CO2 CH4 no gas Polar covalent hydrogen chloride hydrogen sulfide ammonia fluoromethane HCl H2S NH3 CH3F yes Polar and nonpolar covalent Medium sized molecules octane geraniol carvone amylproprionate C8H18 C10H18O C10H14O C8H16O2 liquid (cont.) Unit 2 • Investigation IV

(cont.) (cont.) Substance type Examples Smell? Phase Bonding Size Name Formula Molecular Covalent Large molecules 1-triacontyl palmitate (beeswax) polystyrene (styrofoam) cellulose C46H92O2 C8000H8000 C1800H300O15 00 no solid Ionic Metals bonded to nonmetals sodium chloride (table salt) calcium oxide (lime) calcium carbonate (chalk) NaCl CaO CaCO3 Metallic Elemental metals gold copper aluminum Au Cu Al (cont.) Unit 2 • Investigation IV

Will Smell Won’t Smell Example Chemistry Reasoning A brass doorknob Cu, Zn Sweaty socks hexanoic acid, C6H12O2 Epsom salts magnesium sulfate, MgSO4 Anisyl alcohol in laundry soap C8H10O2 This is a solid substance made of molecules that are so large they will not go into the gas phase under normal conditions. X Sunflower oil C21H38O5 Unit 2 • Investigation IV

Making Sense What general statement(s) can you make about whether a substance will have a smell? (For example: Small polar molecules have a smell.) Unit 2 • Investigation IV

Notes General Ideas about smell: Polarity determines the smell of small molecules. Small polar molecules smell. Small nonpolar molecules do not smell. Polarity does not determine smell in the cases of medium and large molecules. (cont.) Unit 2 • Investigation IV

Notes (cont.) Many solids do not evaporate into gases easily, therefore, solids tend not to smell unless they can become volatile (components of a chocolate bar.) Nonmolecular solids (ionic and metallic solids) do not smell. Medium-sized molecules all seem to smell. (cont.) Unit 2 • Investigation IV

Notes (cont.) Shape and functional group help determine the smell of medium-sized molecules. Large molecules do not smell. They are too big and bulky to become gases and move into the nose. Ionic compounds do not smell – they do not enter the gas phase and travel into the nose like covalently bonded molecules. (cont.) Unit 2 • Investigation IV

Notes (cont.) According to the table, molecules that are gases at ordinary temperatures are composed of very small molecules or of single atoms (such as argon or neon). This is true. According to the table liquids seem to be composed mostly of medium-sized molecules. This is also a fairly consistent generalization, although some liquids do exist that are composed of large, heavy molecules. (cont.) Unit 2 • Investigation IV

Notes (cont.) According to the table, solids are composed of large molecules, ionic compounds, or metallic substances. Of course, we know from experience that some solids sublimate; that is, a few molecules go directly from the solid phase to the gas phase, without passing through the liquid phase. (cont.) Unit 2 • Investigation IV

Chemical Name Common Name Phase Molecular Formula Structural Formula methane natural gas gas CH4 octane gasoline liquid C8H18 polystyrene styrofoam solid (C8H8)n Repeating…. Unit 2 • Investigation IV

Notes (cont.) One of the most important facts you can remember in your study of smell chemistry is that a molecule must be in the gas phase in order to be smelled. Unit 2 • Investigation IV

(repeating throughout the solid in 3 dimensions) Check-In Which of the following molecules will smell? Explain your reasoning. Molecule Structure Phase CaCl2 calcium chloride Cl– Ca2+ Cl– (repeating throughout the solid in 3 dimensions) solid vanillin liquid HCN hydrogen cyanide gas Unit 2 • Investigation IV

Wrap-Up Small molecules smell if they are polar. Medium-sized molecules tend to smell, whether they are polar or not. The smells of medium-sized molecules can be predicted by looking at shape and functional group. (cont.) Unit 2 • Investigation IV

(cont.) Very large molecules do not smell because they do not evaporate and enter the nose. Nonmolecular solids (e.g., salts, metals) do not smell because they do not evaporate. Water is an exception to these generalizations. Humans do not smell water, but conceivably other mammals do. Unit 2 • Investigation IV

Smells Unit – Investigation IV Lesson 8: Take a Deep Breath

ChemCatalyst Name three items that might be on an exam covering the entire Smells Unit. Unit 2 • Investigation IV

The Big Question How well can we predict a molecule's smell, and what factors do we need to consider? Unit 2 • Investigation IV

You will be able to: Switch between the structural formula, Lewis dot structure, and three-dimensional shape of a molecule, and determine the polarity. Unit 2 • Investigation IV

Activity Purpose: The goal of this lesson is to integrate your learning about smell chemistry and to review the entire unit. (cont.) Unit 2 • Investigation IV

(cont.) (cont.) a) Structural formulas… b) Properties…. c) Reasoning… Unit 2 • Investigation IV

(cont.) (cont.) a) Structural formulas… b) Properties…. c) Reasoning… Unit 2 • Investigation IV

(cont.) Unit 2 • Investigation IV

Making Sense (cont.) Has a smell Polar Smallish molecule Shape is non-symmetrical (cont.) Unit 2 • Investigation IV

(cont.) Has a smell polar Non-symmetrical molecule Medium-sized Alcohol Ether (Note: The flat drawing looks symmetrical but the geometry around the O atom is bent.) Unit 2 • Investigation IV

Other possible structural formulas (cont.) Other possible structural formulas (cont.) Unit 2 • Investigation IV

(cont.) Unit 2 • Investigation IV

Check-In Predict the smell for each of the following molecules and explain your reasoning. dimethyl ether decanoic acid Unit 2 • Investigation IV

Wrap-Up No Wrap-Up Unit 2 • Investigation IV