Smells Unit

Smells Unit

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

Smells Unit – Investigation IV

Lesson 1:

Breaking Up Is Hard to Do??

Unit 2 • Investigation IV

© 2004 Key Curriculum Press.

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.)

KeyMoleculesC, H, and O atoms



The Big Question

• Do molecules break apart into atoms when they escape from the smell vial or do they stay together as molecules?



You will be able to:

• Explain smelling in the context of phase change.



C4H8O2

C C C C

H

H

H

H

O

O H

H

H

H

Vial Gbutyric acid

putrid

C C

H

H

O

O C

H

H

H C

H

H

H

Vial Hethyl acetate

sweet

Notes



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.

KeyMoleculesC, H, and O atoms

(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

(cont.)



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.



• 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.

Notes



Check-In

• Examine the following drawing and pick the best explanation from the two below.



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.


Lesson 2:

How Does the Nose Know?



ChemCatalyst

• How do you think your nose detects a smell?



The Big Question

• How does our nose detect different smells?




• Understand how a molecule is detected by the nose.



Activity

Purpose: To design a model that explains how molecules are detected in the nose.



Making Sense

• No Making Sense question.



• 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.

Notes



Check-In

One of the molecules that makes coffee smell is 2-furylmethanethiol:

O

C

C C

C

C

H H

S

H

H

H H • Write down everything you know about

how this molecule is detected by the nose.

• Draw a possible receptor site for this molecule.



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.


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?

Smells SmellsDoesn’t smell?

Here are some of the gases in air: O2 (oxygen), N2 (nitrogen), CO2 (carbon dioxide), Ar (argon).



The Big Question

• In what ways do molecules interact with each other?




• Describe a polar molecule.



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.)



(cont.)

(cont.)



Molecule Results of charged wand test

Molecule Results of charged wand test

water attracted isopropanol

acetic acid hexane

(cont.)



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.



• 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.

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.

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.)

Notes (cont.)



• The attraction that happens between individual polar molecules is called an intermolecular interaction or an intermolecular attraction.

Notes (cont.)



Check-In

• Acetone is polar. Name two other things that are probably true about acetone.



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.


Lesson 4:

Polar Bears and Penguins



ChemCatalyst

Consider the following illustration:

(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.

(cont.)



The Big Question

• How can we explain partial charges on molecules?




• Recognize and explain a polar bond.



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.



Making Sense

• What does electronegativity have to do

with polarity?



• 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.

Notes



• Chemists have a specific name for a molecule that has two poles—it is called a dipole. ("Di" means two.)

Notes (cont.)

(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.

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.

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.

Notes (cont.)



O C O

Notes (cont.)



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.



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.)



• The bonds are labeled nonpolar covalent, polar covalent, and ionic as the difference in electronegativity between the two atoms in the bond increases.

(cont.)


Lesson 5:

Thinking (Electro)Negatively



ChemCatalyst

• Explain how the illustration and the table might relate to each other.



The Big Question

• How does electronegativity relate to polarity and bonding?




• Determine whether a bond is polar, nonpolar, or ionic.



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.)



(cont.)



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.)



(cont.)



• A molecule made from only two atoms is called a diatomic molecule.

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.

Notes (cont.)

(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.

Notes (cont.)



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.



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.


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?



The Big Question

• How does polarity help to explain what is happening between smell molecules and the nose?




• Use polarity to predict whether a molecule will have a smell.



• 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.

Notes



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.)



(cont.)

(cont.)



HCl NH3 H2S CF4

CH2O CClF3 CH4O

(cont.)

(cont.)



Molecule

Has a smell? MoleculeHas a smell?

N2 No NH3 Yes

PH3 Yes HBr Yes

CH4 No CO2 No

H2Se Yes AsH3 Yes

(cont.)



Making Sense

• Explain why polarity might be an important concept to understand when trying to figure out the chemistry of smell.



Notes

(cont.)



N N

C H

H

H

H

O O

C F

F

F

F

O C O

Nonpolar molecules(cont.)

Notes (cont.)



HH

H

P

H H

Se

N HH

H

H Cl

Polar molecules(cont.)

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.

Notes (cont.)



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.)



• Do you think HCN will have a smell? Explain.

(cont.)



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.


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?



The Big Question

• How can we apply what we’ve learned about smell to our daily lives?




• Describe the physical and chemical factors that determine whether on not a type of molecule will smell.



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.)



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

Molecular

Polar covalent

Small molecules

hydrogen chloride

hydrogen sulfide

ammonia

fluoromethane

HCl

H2S

NH3

CH3F

yes gas

Molecular

Polar and nonpolar covalent

Medium sized

molecules

octane

geraniol

carvone

amylproprionate

C8H18

C10H18O

C10H14O

C8H16O2

yes liquid

(cont.)

(cont.)



Substance type Examples Smell? Phase

Bonding Size Name Formula

Molecular

Covalent

Large molecules

1-triacontyl palmitate (beeswax) polystyrene (styrofoam)

cellulose

C46H92O2

C8000H8000

C1800H300O1500

no solid

Ionic

Metals bonded to nonmetals

sodium chloride (table salt)

calcium oxide (lime)

calcium carbonate (chalk)

NaCl

CaO

CaCO3

no solid

Metallic

Elemental metals

gold

copper

aluminum

Au

Cu

Al

no solid

(cont.)

(cont.)



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



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.)



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.)

Notes



• 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.)

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.)

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.)

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.)

Notes (cont.)



Chemical Name

Common Name

Phase Molecular Formula

Structural Formula

methanenatural

gasgas CH4

octane gasoline liquid C8H18

polystyrene styrofoam solid (C8H8)n

Repeating….

C

H

H

H

H

C

H

C C

H

HHH

H

H C

H

C C

H

H

HHH

HH

C C

H

HH

CC C

C CC

C

H

CH2

H

H

H

H

H

CC C

C CC

C

H

H

H

H

H

CH2 CH2

H

etc....etc....



• 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.

Notes (cont.)



Check-In• Which of the following molecules will

smell? Explain your reasoning.

Molecule Structure Phase

CaCl2calcium chloride

Cl– Ca2+ Cl–

(repeating throughout the solid in 3 dimensions) solid

vanillin liquid

HCN

hydrogen cyanidegas

H C N

C

C C

CC

C

C

H

H

HH

H

O

O

H

C

H

H

O



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.)



• 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.

(cont.)


Lesson 8:

Take a Deep Breath



ChemCatalyst

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



The Big Question

• How well can we predict a molecule's smell, and what factors do we need to consider?




• Switch between the structural formula, Lewis dot structure, and three-dimensional shape of a molecule, and determine the polarity.



Activity

Purpose: The goal of this lesson is to integrate your learning about smell chemistry and to review the entire unit.

(cont.)



a) Structural

formulas…

b) Properties….

c) Reasoning…

(cont.)

(cont.)



a) Structural

formulas…

b) Properties….

c) Reasoning…

(cont.)

(cont.)



CC

C

C C

C C

HH

H

H O

O

O C H

H

H

H

(cont.)



Making Sense

C

HO

C

H

H H

CH

O

C

H

H

H

Has a smell

Polar

Has a smell

Polar

Smallish molecule

Polar

Shape is non-symmetrical

Smallish molecule

Polar

Shape is non-symmetrical

(cont.)



CC O H

C

C

H

H

H

H

H

H H

H

H

C C O HC C

H

HH

HH

H

H

H

H

C C O HC C

H

HH

HH

H

H

H

H

Has a smell

polar

Has a smell

polar

Has a smell

polar

Non-symmetrical molecule

Medium-sized

Alcohol


Medium-sized

Ether(Note: The flat drawing looks symmetrical but the geometry around the O atom is bent.)


Medium-sized

Ether

(cont.)



C C O HC C

H

HH

HH

H

H

H

H

CC

O

H

C

C

H

H

H

H

H

H

H

H

H

CC O

H

C

C

H

H

H

H

H

H

H

H

H

C C

O

HC C

H

HH

H

H

H

H

H

H

Other possible structural formulas

(cont.)

(cont.)



CC

C

C C

C C

HH

H

H O

O

O C H

H

H

H

(cont.)



Check-In

• Predict the smell for each of the following molecules and explain your reasoning.

C C

H

H

H

H

H

C C C

H

H

H

H

C C C C C

H

H

H

H

H

H

H

H

H

H

O

O H

decanoic acid

C C

H

O

H

H H

HH

dimethyl ether



Wrap-Up

• No Wrap-Up

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Smells Unit