Smells Unit

1
Smells Unit

• Investigation II Picturing Molecules

Lesson 1 Molecules in Two Dimensions
Lesson 2 Honk If You Like Molecules
Lesson 3 Connect the Dots
Lesson 4 Eight is Enough
Lesson 5 Dots, Dots, and More Dots
Lesson 6 Wheres the Fun?
Lesson 7 Create a Smell
Lesson 8 Making Scents
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Smells Unit Investigation II

• Lesson 1
• Molecules in Two Dimensions

3
ChemCatalyst

• Here are drawings of two molecules that youve
  already smelled. List at least three differences
  and three similarities between the two molecules.

4
The Big Question

• Can the structural formula of a molecule help us
  to predict how it will smell?

5
You will be able to

• Describe a molecule based on its smell.

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Notes

• A structural formula is a drawing or diagram that
  a chemist uses to show how the atoms in a
  molecule are connected.
• Chemists refer to the connections between atoms
  in a molecule as a bond. In structural formulas,
  the covalent bonds are represented as lines.

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Activity

• Purpose In this lesson you are introduced to the
  structural formulas of the molecules you have
  smelled plus some new molecules. You will look
  for patterns in the ways the atoms are connected.

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Making Sense

• What structural features seem to be the best
  predictors of the smell of a molecule?

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Notes
(cont.)
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Notes (cont.)

• Functional groups are structural features that
  show up repeatedly in molecules and seem to
  account for some of their chemical properties.

(cont.)
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Notes (cont.)
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Check-In

• If a molecule is sweet, what other things do you
  know about it? List at least four things that are
  probably true.

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Wrap-Up

• Structural formulas show how the atoms in a
  molecule are put together.
• Certain structural features in molecules called
  functional groups appear to be related to smell.

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Smells Unit Investigation II

• Lesson 2
• Honk If You Like Molecules

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ChemCatalyst

• Examine the following molecules. What patterns do
  you see in the bonding of hydrogen, oxygen,
  carbon, and nitrogen?

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The Big Question

• How can HONC 1234 help us to draw structural
  formulas?

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You will be able to

• Determine whether the structural formula of a
  given molecule is possible.

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Notes

• HONC 1234 is a simple, catchy phrase reminding us
  about the bonding of hydrogen, oxygen, nitrogen
  and carbon. This easy-to-remember phrase reminds
  us how many bonds each element usually makes
  within a molecule.

(cont.)
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Notes (cont.)

• Double bonds and triple bonds still follow the
  HONC 1234 rule. The double-bonded oxygen in the
  menthone molecule is bonded twice to carbon and
  therefore follows the guidelines.

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Activity

• Purpose The purpose of this activity is to give
  you practice in creating structural formulas from
  molecular formulas and to help you begin to
  understand why atoms end up in the specific
  arrangements we find them in.

(cont.)
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(cont.)

• Molecular formula 1 C3H8
• Molecular formula 2 C3H8O
• Molecular formula 3 C3H9N

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Making Sense

• The third molecular formula has at least three
  possible structures. Are these all the same
  molecule? Explain.

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Notes

• Molecular formula 1 (the same molecule drawn
  with two different orientations)

(cont.)
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Notes (cont.)

• Molecular formula 2 (four different drawings are
  shown three different molecules are represented)

(cont.)
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Notes (cont.)

• Molecular formula 3 (four different drawings are
  shown however, they represent only three
  different structures)

(cont.)
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Notes (cont.)

• Molecules are isomers of one another if they have
  the same molecular formula but different
  structural formulas.

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Check-In

• Are the following molecules correct according to
  HONC 1234? If not, what specifically is wrong
  with them?
• 1. 2.

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Wrap-Up

• The HONC 1234 rule tells us how many times
  hydrogen, oxygen, nitrogen and carbon tend to
  bond.
• When a molecule is oriented differently in space
  it is still the same molecule.
• A molecular formula can be associated with more
  than one distinct structural formula.

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Smells Unit Investigation II

• Lesson 3
• Connect the Dots

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ChemCatalyst

• This is a drawing of the structural formula of a
  methane molecule. The lines represent bonds.
  Explain what you think a bond is.

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The Big Question

• How can Lewis dot symbols help us to understand
  and predict bonding?

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You will be able to

• Draw the Lewis dot symbol for an element and
  predict how many covalent bonds it will make.

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Notes

• A covalent bond is a connection that forms
  between two atoms when those atoms are sharing a
  pair of electrons between them.

(cont.)
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Notes (cont.)

• When we draw an atom using dots to represent the
  valence electrons it is called a Lewis dot
  symbol.
• When we draw a molecule using dots to represent
  the valence electrons it is called a Lewis dot
  structure.

(cont.)
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Notes (cont.)

• Nitrogen, with five valence electrons, would be
  drawn as follows

• Notice that the Lewis dot symbol of nitrogen has
  three unpaired electrons and one electron pair.
  This means that nitrogen has three electrons that
  can potentially be paired up with electrons from
  other atoms.

(cont.)
36
Notes (cont.)
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Activity

• Purpose In this lesson you will begin to
  understand why atoms connect to each other the
  way they do. You will be introduced to a tool,
  called Lewis dot symbols, which will assist you
  in building molecules and predicting how many
  bonds an element will have.

(cont.)
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(cont.)

• C N O F
  Ne
• Si P S Cl
  Ar

(cont.)
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(cont.)
Group number IV V VI VII VIII
Number of bonds
First row elements C N O F Ne
Second row elements Si P S Cl Ar
(cont.)
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(cont.)
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Making Sense

• Based on what youve learned in this lesson,
  explain why the HONC 1234 rule works.

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Notes
(cont.)
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Notes (cont.)

• Bonded pair refers to a pair of electrons that
  are involved in bonding between two different
  atoms.
• Lone pair refers to a pair of electrons that are
  not involved in bonding but are paired up within
  an atom.
• A single electron is sometimes referred to as an
  unpaired electron.

lone pair of electrons
bonded pair of electrons
44
Check-In

• Draw the Lewis dot symbol for the element I,
  iodine. Explain how you arrived at your
  particular drawing.
• How many covalent bonds does iodine make?

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Wrap-Up

• A covalent bond is one in which two atoms share
  valence electrons.
• In a Lewis dot structure, pairs of electrons that
  are not bonded are referred to as lone pairs.
• HONC 1234 indicates how many unpaired electrons
  are associated with hydrogen, oxygen, nitrogen
  and carbon.

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Smells Unit Investigation II

• Lesson 4
• Eight is Enough

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ChemCatalyst

• Draw the Lewis dot structure for the following
  covalently bonded molecule. Explain how you
  arrived at your answer.
• Cl2

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The Big Question

• How can we use Lewis dot structures to help draw
  structural formulas?

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You will be able to

• Predict whether a given compound would be stable
  and likely to be found in nature.

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Notes
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Activity

• Purpose In this lesson you will use Lewis dot
  structures to create structural formulas of
  molecules containing elements in addition to H,
  O, N, and C. You will look for patterns in the
  number of electrons surrounding each atom in a
  Lewis dot structure in order to develop further
  understanding of bonding.

(cont.)
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(cont.)
Br2 H2S PH3 SiH4

(cont.)
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(cont.)
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Making Sense

• The noble gases do not form bonds with other
  atoms (except under very extreme conditions).
  Explain why you think this might be true (use
  your Lewis dot structures).

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Notes

• Atoms of most elements are very reactive.
• They become stable (the opposite of reactive)
  when they combine with other atoms to form
  compounds.
• The more stable a molecule is, the more likely we
  are to find that it exists in nature.
• The octet rule states that atoms tend to form
  bonds by sharing valence electrons until eight
  valence electrons surround each atom.

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Check-In

• Which of the following formulas satisfy the HONC
  1234 rule?
• Which of the following formulas satisfy the octet
  rule?
• Which of the following formulas represent stable
  compounds we might find in the world around us?
• a) CH3 b) CH4

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Wrap-Up

• Elements form bonds by sharing electrons until
  each atom has the same number of valence
  electrons as the noble gas in the same row of the
  periodic table this is called the octet rule.

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Smells Unit Investigation II

• Lesson 5
• Dots, Dots, and More Dots

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ChemCatalyst

• Here are the structural formulas for N2 (nitrogen
  gas), O2 (oxygen gas), and F2 (fluorine gas).
  Draw the Lewis dot structures for these three
  molecules.

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The Big Question

• How do we draw a Lewis dot structure for a
  molecule?

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You will be able to

• Use Lewis dot symbols to draw a possible
  structure for a C2H4O2 molecule.

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Notes

• Draw Lewis dot symbols for C and two O atoms
• Bring atoms together
• Create double bonds

63
Activity

• Purpose In this lesson you will work to create
  structural formulas for various molecules. You
  will start with the Lewis dot structures of
  individual atoms. These atoms can then be
  arranged in more than one way to create
  molecules. Finally, structural formulas will be
  translated from the Lewis dot representations.

(cont.)
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(cont.)
Start with these atoms Draw the Lewis structure for the starting atoms Add hydrogen atoms to satisfy the octet rule How many Hs are needed? Draw the structural formula for the molecule Write the molecular formula for the molecule
2 carbon atoms bonded together
1 carbon atom and 1 oxygen atom
1 carbon atom and 1 nitrogen atom
1 carbon atom and 2 oxygen atoms
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Making Sense

• Explain how HONC 1234 assists you in checking out
  the structural formulas you create.

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Check-In

• We know two things about a certain molecule. We
  know that its molecular formula is C2H4O2 and we
  know that it has one CO in it. Using Lewis dot
  symbols and the octet rule to guide you, draw at
  least one possible structure for this molecule.
  (There are a total of three possible.)

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Wrap-Up

• Atoms can form double and triple bonds to satisfy
  the octet rule.

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Smells Unit Investigation II

• Lesson 6
• Wheres the Fun?

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ChemCatalyst

• The following two molecules have the same
  molecular formula, C8H16O2. They also have
  similar properties.
• How are their structural formulas similar?
• How are their structural formulas different?

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Notes
methyl heptanoate boiling point 174 C smell fruity (berry)
propyl pentanoate boiling point 167.5 C smell fruity (apple, pineapple)
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The Big Question

• How are molecular structure and molecular
  properties related?

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You will be able to

• Identify some common functional groups in a large
  molecule.

73
Activity

• Purpose The structure of a molecule determines
  its properties. Even slight changes in structure
  can result in significant changes in property. In
  this activity you will be asked to examine the
  relationships between the structures and
  properties of a specific set of molecules. From
  these data you should be able to predict the
  properties of new molecules based on their
  structures alone.

(cont.)
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(cont.)
(cont.)
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(cont.)
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Making Sense

• 1. What kinds of molecular features did you use
  to predict the boiling point and smell of these
  five molecules?
• 2. What molecular features did the following
  molecules have in common?
• a) Molecules that smell fishy
• b) Molecules that smell putrid
• c) Molecules with a boiling point range of 49-69
  degrees

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Notes
78
Check-In

• Group the following molecules according to their
  smell.
• a. Which ones will have similar smells?
• b. What smells would you predict for the groups
  and why?

(cont.)
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(cont.)
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Wrap-Up

• Molecules with the same functional groups have
  similar boiling points as well as similar smells.
• The structural features of a molecule are largely
  responsible for the chemical behavior of the
  molecule.

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Smells Unit Investigation II

• Lesson 7
• Create a Smell

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ChemCatalyst

• What are some of the starting ingredients you
  will be using in this lab?
• Name something you will be doing to the chemicals
  in this experiment.

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The Big Question

• How do chemists create the smells they want in
  the laboratory?

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You will be able to

• Determine whether two molecules with distinct
  smells can combine to produce a molecule with a
  different smell.

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Activity

• Purpose You will be working in the lab to create
  new smells.
• Purpose Todays lesson is a formal laboratory
  experiment. You should have read the pre-lab and
  become acquainted with the experimental procedure
  before todays class. You will be working in the
  lab to create new smells.

(cont.)
86

• Safety Precautions
• Dress appropriately for a chemistry lab and
  always wear goggles.
• There should be NO OPEN FLAMES because the
  organic chemicals are flammable.
• Extreme care should be taken when handling 18-M
  sulfuric acid. It burns the skin and creates
  holes in clothing.
• Heating must be done slowly and carefully. When
  heating is finished, hot plates should be turned
  off immediately.
• During clean-up place the final products in
  designated waste containers.

(cont.)
87
(cont.)
Test Tube Organic Acid Alcohol
1 acetic acid isoamyl alcohol
2 acetic acid butyl alcohol
3 butyric acid ethyl alcohol
(cont.)
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(cont.)
Test Tube Smell of Organic Acid Smell of Alcohol Smell of Mixture Before Heating Smell of Mixture After Heating
1
2
3
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Making Sense

• What functional group do you think is present in
  the final molecules? Explain.
• What do you think happened to the molecules to
  change the smell?

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Check-In

• No Check-In.

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Wrap-Up

• Two molecules with distinct smells can combine to
  produce a new molecule(s) with a different smell.

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Smells Unit Investigation II

• Lesson 8
• Making Scents

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ChemCatalyst

• What do you think happened in yesterdays
  experiment to transform an acid molecule and an
  alcohol molecule into a sweet smelling molecule?

94
The Big Question

• What happened in the test tubes to create new
  substances?

95
You will be able to

• Predict the product of a chemical reaction.

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Notes

• A chemical reaction (rxn) is defined as a
  chemical transformation or change that occurs
  when substances interact to produce new
  substances with new properties.
• A chemical reaction is the same as a chemical
  change.
• The starting ingredients in a chemical reaction
  are called the reactants.
• The ending compounds are called the products.

(cont.)
97
Notes (cont.)

• When chemists show the reactants and the products
  in a chemical sentence like thisit is called
  a chemical equation.
• A catalyst is a substance added to a reaction
  that accelerates that chemical reaction but is
  not itself consumed or altered by the reaction.

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Activity

• Purpose This lesson will assist you in
  processing and making sense of the experiment you
  just completed. By examining the structural
  formulas of the starting ingredients, you will be
  able to see how the molecules broke apart and
  recombined to create the sweet-smelling products.

(cont.)
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(cont.)
(cont.)
100
(cont.)
(cont.)
101
(cont.)
isoamyl acetate
(cont.)
102
(cont.)
ethyl butyrate
(cont.)
103
(cont.)
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Making Sense

• Use your own words to describe what you think
  happened on a molecular level to the two
  compounds that took part in this reaction.

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Notes (cont.)
106
Check-In

• Predict the structural formula of the product of
  the following reaction.
• What is missing from the equation?
• What smell would you expect?
• Could you figure out the name of the product?

107
Wrap-Up

• The smell of the molecules in the ester lab
  changed because the reactant molecules combined
  to form different molecules.