Smells Unit

Smells Unit

Investigation III: Building MoleculesLesson 1: New Smells, New IdeasLesson 2: Molecules in Three DimensionsLesson 3: Two’s CompanyLesson 4: Let’s Build ItLesson 5: Shape MattersLesson 6: What Shape Is That Smell?Lesson 7: Sorting It Out

Smells Unit – Investigation III

Lesson 1:

New Smells, New Ideas

Unit 2 • Investigation III

© 2004 Key Curriculum Press.

ChemCatalyst

• Do you think any of these molecules will smell similar? What evidence do you have to support your prediction?

(cont.)



citronellolC10H20O

C C

C

C C C C

C

C C O

H

H

H

H H

H

H H

H

H

H

H

H

H

H

H

H

H

H

H

geraniolC10H18O

C C

C

C C C C

C

C C O

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H H

H

H

mentholC10H20O

C

CC

C

C C

CC

C

C

H

H

H

H

HH

H

H

H

H

H

H

H

H

H

H

H

H

O

H

H

(cont.)



The Big Question

How do we refine our hypothesis about how smell works?



You will be able to:

• Evaluate the usefulness of functional groups in predicting the smell of a molecule.



Activity

Purpose: In this lesson you will be introduced to five new molecules. These molecules will lead you in the direction of new discoveries about the relationship between smell and chemistry.

(cont.)



Vial Molecular formula

and name

Functional group

Structural formula Actual Smell

O C10H20O

citronellol

alcohol

P C10H18O

fenchol

alcohol

Q C10H18O

geraniol

alcohol

C C

C

C C C C

C

C C O

H

H

H

H H

H

H H

H

H

H

H

H

H

H

H

H

H

H

H

C

C

C

C

C

C

C

C

C

C

O

HH

H

H

H

H

H

H

H

H H

H

H

H

H

H

H H

C C

C

C C C C

C

C C O

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H H

H

H



Vial Molecular formula

and name

Functional group

Structural formula Actual Smell

R C10H20O

menthol

alcohol

S C10H18O

borneol

alcohol

C

CC

C

C C

CC

C

C

H

H

H

H

HH

H

H

H

H

H

H

H

H

H

H

H

H

O

H

H

C

C

C

C

C

C

C

H

H

H

H

H

CC H

H

H

H

H

H

O

H

C

H

H H

HH

H

(cont.)



Making Sense

Review the results of the smell investigation to date by indicating on the following chart:

(1) how molecular formulas can be used to predict smell, (2) how name can be used to predict smell, (3) how functional group can be used to predict smell, (4) what other information might be important. Examples are given for molecules that smell fishy.

(cont.)



smell

Molecular Formula1 N = fishy

Chemical Name“ine” = fishy

Functional Groupamine = fishy

Another property of molecules?

SmellsSummary Chart



Check-In

• No Check-In.



Wrap-Up

• Molecular formula and functional group are not always sufficient information to predict the smell of a molecule accurately.

• It appears that the overall shape of a molecule may be related to its smell.


Lesson 2:

Molecules in Three Dimensions



ChemCatalyst

• This is a new way to represent one of the molecules that you smelled in the last class. Which molecule is this? Give your reasoning.

Molecule #1sweet



The Big Question

• Why do some molecules with the same functional group have different smells?




• Name some differences between a structural formula and a ball-and-stick model.



• A ball-and-stick model is a 3-dimensional model that a chemist uses to show how the atoms in a molecule are arranged in space.

Notes (cont.)



Activity

Purpose: In this class you will be introduced to 3-dimensional molecular models. These particular molecular models are called ball-and-stick models. This type of model gives us more information than a structural formula. It shows how the atoms in a molecule are arranged in space.

(cont.)



Molecule #1Sweet smelling (cont.)

(cont.)



Molecule #2Minty smelling (cont.)

(cont.)



Molecule #3Camphor smelling

(cont.)



Making Sense

• What information do you need to know about a molecule in order to build a ball-and-stick model of it?



Check-In

• List the molecular model pieces you would need to build a model of ethanol—C2H6O.



Wrap-Up

• A ball-and-stick model is a 3-dimensional representation of a molecule that shows us how the atoms are arranged in space in relationship to one another.

• Molecules have complex 3-dimensional shapes. The atoms are not necessarily lined up in straight lines and molecules are not flat as depicted in a structural formula.


Lesson 3:

Two’s Company



ChemCatalyst

• Here is the structural formula of ethanol. Which is the correct ball-and-stick model for ethanol? Explain your reasoning.

C C HOH

H H

H H (cont.)



1.

2.

3.

4.

(cont.)



The Big Question

• Why are molecules in a ball-and-stick model crooked rather than straight?




• Build a ball-and-stick model showing lone pair electrons for a molecule.



• Electron pairs are sometimes called bonded pairs. Both of these terms are a bit inaccurate because not all covalent bonds consist of a pair of electrons.

• Electron charge is another area of potential confusion. We cannot fully explain why two particles with identical negative charges remain in such close proximity to one another within a covalent bond.

Notes



• Sets of electrons that remain together in bonds or in lone pairs are referred to as electron domains. Electron domains “prefer” to be as far apart as possible from each other.

Notes (cont.)



Activity

Purpose: In this class you will gain practice creating three dimensional models of some small molecules. The concept of electron domains helps to explain why molecules actually exist in crooked and bent shapes, rather than straight lines.

(cont.)



CH4 NH3 H2O

(cont.)



Making Sense

• Explain how the lone pairs affect the shape of your molecules.



• The underlying shape in all three of the molecules we created today is called tetrahedral.

• A paddle represents a lone pair.

Notes



C

H

H

H

H

N

H

H

H

O

HH

CH4 NH3 H2O

Notes (cont.)



Check-In

• Build a model for HF. Be sure to show all of the lone pairs.

• Build a model for Ne. Be sure to show all of the lone pairs.



Wrap-Up

• Electron domains represent the space occupied by bonded electrons or a lone pair.

• Electron domains are located as far apart from one another as possible.

• The 3-dimensional shape of a molecule is determined by both bonding electrons and lone pairs.


Lesson 4:

Let’s Build It



ChemCatalyst

• Remove the lone pair paddles from all five models. Now describe the remaining geometric shape.

C

H

H

H

H

N

H

H

H

O

HH H

F Ne

CH4 NH3 H2O HF Ne



The Big Question

• How do we describe the shape of a large molecule?




• Predict the shape of a molecule.



C

H

H

H

H

N

H

H

H

O

HHH

FNe

tetrahedral pyramidal bent linear point

Notes

(cont.)



• Lone-pair paddles are not generally included in ball-and-stick models. We have included them in order to illustrate how lone pairs affect molecular shape.

• A linear molecule has three atoms in a row, with two electron domains around the central atom.

(cont.)

Notes (cont.)



• A trigonal planar shape is flat and consists of four atoms bonded together in a single plane. The central atom is bonded to three atoms but unlike ammonia there are only three electron domains in these molecules as shown below.

3 electron domains

A model of a trigonal planarmolecule as seen from above.

Notes (cont.)



Activity

Purpose: In this lesson you gain practice creating actual ball-and-stick models from molecular formulas, using Lewis dot structures to assist you.

(cont.)



Molecular Formula

Lewis Dot Structure

Describe/Draw Shape

methane: CH4

tetrahedral

water: H2O

bent

ethane: C2H6

OH H

C

H

H

H

H



Molecular Formula

Lewis Dot Structure

Describe/Draw Shape

chloromethane:CH3Cl

dichloromethane:

CH2Cl2

methanol:CH3OH



Molecular Formula

Lewis Dot Structure

Describe/Draw Shape

methyl amine: CH3NH2

formaldehyde: CH2O

ethene (ethylene): C2H4



Molecular Formula

Lewis Dot Structure

Describe/Draw Shape

hydrogen cyanide: HCN

ethyne (acetylene): C2H2



Mak

ing

Sen

seNumber of

domains

Number of

lone pairs

Shape Example Sketch

4 0 tetrahedral CH4

4 1 pyramidal NH3

4 2 bent H2O

3 0 trigonal

planar

CH2O

2 0 linear CO2C OO

C

H

H

H

H

N

H

H

H

HH

O

C

H

H

O



Check-In

• What is the shape of the following molecule?

H2S



Wrap-Up• Knowing the Lewis dot structure of a

molecule allows one to predict its 3-dimensional shape.

• The shape of large molecules is determined by the smaller shapes around individual atoms.

• While lone pairs affect the positions of the atoms, they are not included in describing the shape of a molecule. The shape refers only to the positions of the atoms.


Lesson 5:

Shape Matters



ChemCatalyst

• Write chemical formulas for the following two molecules.

• Are these two representations of the same molecule? Why or why not?

• Do you expect these two molecules to have similar properties? Why or why not?

C

O

H

maleic acid fumaric acid



The Big Question

• What evidence suggests that chemical properties are related to the shape of a molecule?




• Name some chemical properties that are related to shape.



Activity

Purpose: To compare the properties of maleic acid and fumaric acid, two compounds with identical molecular formulas.

Safety note: Everyone will wear safety goggles at all times.

(cont.)



thymol blue

magnesium

sodium carbonate

maleic acid

fumaric acid

(cont.)

(cont.)



Property Maleic Acid (C4H4O4) Fumaric Acid (C4H4O4)

Solubility

Reaction with thymol blue

Reaction with magnesium

Reaction with Na2CO3

(cont.)



Making Sense

• What evidence do you have that molecular shape is related to chemical properties?



• The H atoms on the C atoms on either side of the double bond can both point in the same direction or they can point in opposite directions. These two forms are called isomers.

• The form with both H atoms pointing in the same direction is referred to as the cis isomer.

• When the H atoms point in opposite directions, the isomer is referred to as a trans isomer.

Notes



Check-In

• No Check-In.



Wrap-Up

• Chemical properties are related to shape.

• Twisting (or rotation of) the ends of a molecule around a C=C double bond is restricted.

• Isomers are molecules with the same chemical formula but different shapes.


Lesson 6:

What Shape Is That Smell?



ChemCatalyst

• What obvious differences do you see between these two different types of models?

space-filling model of citronellol

ball-and-stick model of citronellol



The Big Question

• Is there a relationship between the 3-dimensional shape of a molecule and its smell?




• Discuss how the three-dimensional model of a molecule relates to its structural formula.



• A space-filling model is a 3-dimensional model that a chemist uses to show how the atoms are arranged in space and how they fill this space.

Notes



Activity

Purpose: In this lesson you will be introduced to space-filling models of six molecules. By comparing and contrasting these models, you will learn more about the relationship between smell and chemistry.

(cont.)



Questions: Molecule #1

and #6 - sweet

Molecule #3

and #4 - minty

Molecule #5 and

#2 - camphor

1. Using the molecular information sheets from Lesson III-1, identify the molecules in the photos.

2. What similarities do you notice?

3. How would you describe the overall shape of the entire molecule for both molecules in the set?

(cont.)



Questions: One molecule from each set (for example, #1, #3,

and #5)

4. What similarities do you notice?

5. What major differences do you notice?

6. If you were to describe the overall shapes of the three molecules, what words would you use?

(cont.)



Making Sense

• On the basis of your examination of these space-filling models, do you think there is a connection between molecular shape and smell? Provide evidence for your answer.



• These three larger shapes are referred to as stringy, flat, and ball-shaped.

• Sweet smells are associated with stringy molecules, minty smells are associated with flat molecules, and camphor smells are associated with ball-shaped molecules.

Notes



Check-In

• What smell do you predict for the substance in Vial V? Explain your reasoning.

(cont.)



Vial V

1. Molecular formula: C12H20O2

2. Chemical name: bornyl acetate

3. Structural formula:

4. Molecular model:

C

C

C

C

C

C

CH

H

H

H

HCC HH

H

HH

H

H

C

H

H H

H

HOC

O

C

H

H

H



• A pheromone is a chemical substance that is produced by an animal and serves as a form of chemical communication to other individuals of the same species, often stimulating specific behavioral responses.

• It is called an aggregation pheromone because it causes large numbers of insects to collect in one place.

Notes



Wrap-Up

• Space-filling models provide another way of looking at the 3-dimensional shape of molecules—one that represents the space occupied by atoms.

• Smell appears to be directly related to the 3-dimensional molecular shape of a substance.


Lesson 7:

Sorting It Out



ChemCatalyst

• What smell(s) do you predict for a stringy molecule? Explain your reasoning.



The Big Question

• What chemical information is most useful in predicting smell?




• Predict the smell of a mystery molecule.



Activity

Purpose: In this lesson you will try to determine which pieces of chemical information are most valuable in determining the smell of a molecule. You will examine information on all of the smell molecules you’ve encountered so far, in order to come up with specific relationships between chemical information and the five smell categories.

(cont.)



Smell Classification

Shape(s) Functional Group(s)

Molecular Formula(s)

Sweet

Minty

Camphor

Putrid

Fishy

(cont.)



Making Sense

• In what ways are shape, functional group, and molecular formula related to smell?



Sweet:

Minty:

Camphor:

Fishy:

Putrid:

Notes



Check-In

• Write down the number on your Mystery Card.

• Predict the smell of the mystery molecule.

• Explain your reasoning.



Wrap-Up

• Molecular shape can be used to predict smells for esters, alcohols, ketones, and aldehydes.

• Amines and carboxylic acids have distinctive smells.

• For stringy molecules it is necessary to look at functional group as well as molecular shape in order to determine smell.

Documents

Smells Unit