Smells Unit

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Smells Unit

• Investigation III Building Molecules

Lesson 1 New Smells, New Ideas
Lesson 2 Molecules in Three Dimensions
Lesson 3 Twos Company
Lesson 4 Lets Build It
Lesson 5 Shape Matters
Lesson 6 What Shape Is That Smell?
Lesson 7 Sorting It Out
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Smells Unit Investigation III

• Lesson 1
• New Smells, New Ideas

3
ChemCatalyst

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

(cont.)
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(cont.)
5
The Big Question

• How do we refine our hypothesis about how smell
  works?

6
You will be able to

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

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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.)
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Vial Molecular formula and name Functional group Structural formula Actual Smell
O C10H20O citronellol alcohol
P C10H18O fenchol alcohol
Q C10H18O geraniol alcohol
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(cont.)
Vial Molecular formula and name Functional group Structural formula Actual Smell
R C10H20O menthol alcohol
S C10H18O borneol alcohol
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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.)
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(No Transcript)
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Check-In

• No Check-In.

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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.

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Smells Unit Investigation III

• Lesson 2
• Molecules in Three Dimensions

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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 1 sweet
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The Big Question

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

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You will be able to

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

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Notes (cont.)

• 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.

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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.)
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(cont.)
Molecule 1 Sweet smelling
(cont.)
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(cont.)
Molecule 2 Minty smelling
(cont.)
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(cont.)
Molecule 3 Camphor smelling
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Making Sense

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

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Check-In

• List the molecular model pieces you would need to
  build a model of ethanolC2H6O.

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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.

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Smells Unit Investigation III

• Lesson 3
• Twos Company

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ChemCatalyst

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

(cont.)
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(cont.)
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The Big Question

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

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You will be able to

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

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Notes

• 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.

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Notes (cont.)

• 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.

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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.)
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(cont.)

• CH4 NH3 H2O

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Making Sense

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

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Notes

• The underlying shape in all three of the
  molecules we created today is called tetrahedral.
• A paddle represents a lone pair.

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Notes (cont.)
CH4
NH3
H2O
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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.

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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.

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Smells Unit Investigation III

• Lesson 4
• Lets Build It

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ChemCatalyst

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

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The Big Question

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

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You will be able to

• Predict the shape of a molecule.

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Notes
(cont.)
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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.)
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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.

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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.)
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Molecular Formula Lewis Dot Structure Describe/Draw Shape
methane CH4 tetrahedral
water H2O bent
ethane C2H6
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Molecular Formula Lewis Dot Structure Describe/Draw Shape
chloromethaneCH3Cl
dichloromethane CH2Cl2
methanolCH3OH
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Molecular Formula Lewis Dot Structure Describe/Draw Shape
methyl amine CH3NH2
formaldehyde CH2O
ethene (ethylene) C2H4
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Molecular Formula Lewis Dot Structure Describe/Draw Shape
hydrogen cyanide HCN
ethyne (acetylene) C2H2
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Making Sense
Number 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 CO2
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Check-In

• What is the shape of the following molecule?
• H2S

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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.

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Smells Unit Investigation III

• Lesson 5
• Shape Matters

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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?

maleic acid
fumaric acid
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The Big Question

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

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You will be able to

• Name some chemical properties that are related to
  shape.

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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.)
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maleic acid
fumaric acid
(cont.)
thymol blue
magnesium
sodium carbonate
(cont.)
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(cont.)
Property Maleic Acid (C4H4O4) Fumaric Acid (C4H4O4)
Solubility
Reaction with thymol blue
Reaction with magnesium
Reaction with Na2CO3
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Making Sense

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

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Notes

• 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.

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Check-In

• No Check-In.

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Wrap-Up

• Chemical properties are related to shape.
• Twisting (or rotation of) the ends of a molecule
  around a CC double bond is restricted.
• Isomers are molecules with the same chemical
  formula but different shapes.

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Smells Unit Investigation III

• Lesson 6
• What Shape Is That Smell?

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ChemCatalyst

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

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The Big Question

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

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You will be able to

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

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Notes

• 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.

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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.)
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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.)
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(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?
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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.

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Notes

• 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.

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Check-In

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

(cont.)
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Vial V 1. Molecular formula C12H20O2 2.
Chemical name bornyl acetate 3. Structural
formula 4. Molecular model
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Notes

• 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.

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Wrap-Up

• Space-filling models provide another way of
  looking at the 3-dimensional shape of
  moleculesone that represents the space occupied
  by atoms.
• Smell appears to be directly related to the
  3-dimensional molecular shape of a substance.

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Smells Unit Investigation III

• Lesson 7
• Sorting It Out

81
ChemCatalyst

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

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The Big Question

• What chemical information is most useful in
  predicting smell?

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You will be able to

• Predict the smell of a mystery molecule.

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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 youve encountered so far, in order to
  come up with specific relationships between
  chemical information and the five smell
  categories.

(cont.)
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(cont.)
Smell Classification Shape(s) Functional Group(s) Molecular Formula(s)
Sweet
Minty
Camphor
Putrid
Fishy
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Making Sense

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

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Notes

• Sweet
• Minty
• Camphor
• Fishy
• Putrid

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Check-In

• Write down the number on your Mystery Card.
• Predict the smell of the mystery molecule.
• Explain your reasoning.

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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.