Smells Unit

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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
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Smells Unit Investigation IV

• Lesson 1
• Breaking Up Is Hard to Do??

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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
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The Big Question

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

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You will be able to

• Explain smelling in the context of phase change.

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Notes
C4H8O2
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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.)
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(cont.)
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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.

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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.

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Check-In

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

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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.

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Smells Unit Investigation IV

• Lesson 2
• How Does the Nose Know?

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ChemCatalyst

• How do you think your nose detects a smell?

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The Big Question

• How does our nose detect different smells?

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You will be able to

• Understand how a molecule is detected by the nose.

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Activity

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

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Making Sense

• No Making Sense question.

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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.

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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.

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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.

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Smells Unit Investigation IV

• Lesson 3
• Attractive Molecules

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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?

Doesnt smell?
Smells
Smells
Here are some of the gases in air O2 (oxygen),
N2 (nitrogen), CO2 (carbon dioxide), Ar (argon).
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The Big Question

• In what ways do molecules interact with each
  other?

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You will be able to

• Describe a polar molecule.

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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.

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(cont.)
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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.

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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.

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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.)
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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.)
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Notes (cont.)

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

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Check-In

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

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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.

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Smells Unit Investigation IV

• Lesson 4
• Polar Bears and Penguins

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ChemCatalyst

• Consider the following illustration

(cont.)
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(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.

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The Big Question

• How can we explain partial charges on molecules?

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You will be able to

• Recognize and explain a polar bond.

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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.

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Making Sense

• What does electronegativity have to do with
  polarity?

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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.

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Notes (cont.)

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

(cont.)
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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.

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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.

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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.

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Notes (cont.)
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Check-In

• Is the bond between these atoms polar? Explain
  your reasoning.
• How would the atoms be portrayed in the comic
  bookas polar bears, penguins, or both? Explain.

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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.)
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(cont.)

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

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Smells Unit Investigation IV

• Lesson 5
• Thinking (Electro)Negatively

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ChemCatalyst

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

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The Big Question

• How does electronegativity relate to polarity and
  bonding?

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You will be able to

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

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Activity

• Purpose This lesson explores electronegativity
  in a quantitative fashionthat 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.)
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(cont.)
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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.)
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(cont.)
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Notes

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

(cont.)
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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.)
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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.

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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.

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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.

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Smells Unit Investigation IV

• Lesson 6
• I Can Relate

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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?

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The Big Question

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

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You will be able to

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

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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.

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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.)
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Making Sense

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

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Notes
(cont.)
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Notes (cont.)
Nonpolar molecules
(cont.)
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Notes (cont.)
Polar molecules
(cont.)
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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.

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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.)
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(cont.)

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

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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.

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Smells Unit Investigation IV

• Lesson 7
• Sniffing It Out . . .

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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 wont
  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?

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The Big Question

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

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You will be able to

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

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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.)
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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.)

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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.)
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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.)
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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.)
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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.)
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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.)
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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.

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Check-In

• Which of the following molecules will smell?
  Explain your reasoning.

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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.)
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(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.

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Smells Unit Investigation IV

• Lesson 8
• Take a Deep Breath

102
ChemCatalyst

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

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The Big Question

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

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You will be able to

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

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Activity

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

(cont.)
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Making Sense
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(cont.)
Other possible structural formulas
(cont.)
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(cont.)
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Check-In

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

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Wrap-Up

• No Wrap-Up