CHEMISTRY NOW: Molecules, Isomers and Our World (Grades 5-8) Print

Objective:

stdents will understand that the three-dimensional structure of molecules affects their reactivity to introduce the concept of isomers to connect three-dimensional structure of molecules to fields of modern science and technology


Introduction Notes:

CHEMISTRY NOW: Molecules, Isomers and Our World

 

Subject Area: Chemistry

Grade Level:  Middle School Chemistry

Lesson Title: Molecules, Isomers and Our World

National Science Standards:
Science as Inquiry: 5-8

Physical Science Standards:

Content Standard B: Properties of Matter

 

Suggested Prior Knowledge:  particles of matter, physical and chemical changes, physical and chemical properties

 

Purpose: To give students an understanding that the three-dimensional structure of a molecule or "shape"  plays a role in reactivity and chemical properties, and is therefore relevant to science and technology industries.

Key Vocabulary: 

chemical property: a chemical property is any of a material's properties that becomes evident during a chemical reaction. Chemical properties are determined from their action with other substances. For example, water is a polar molecule and can dissolve like substances.

physical property:a characteristic that can be determined without changing the chemical make-up of a substance. For example, color and texture of a compound.

      molecule: a unit of matter that results when two or more atoms are joined by bonds

molecular formula:a formula that tells the actual number of atoms in a molecule

isomers:molecules that have the same number and types of atoms, but are arranged differently

Objectives:

1.     students will understand that the three-dimensional structure of molecules affects their reactivity

2.     to introduce the concept of isomers

3.     to connect three-dimensional structure of molecules to fields of modern science and technology

Materials:

Student worksheet

Mirror

Pair of gloves

Caraway seeds

Mint leaves (fresh or dried)

2 small bowls and 2 spoons per group of 4-5

Washable Markers

Procedure:

Begin with an introduction of what the students will be learning about during the course of this lesson. Tell students that today we will be learning about the importance of molecular shape in chemistry. This means how a molecule is organized and what it looks like. Initiate a conversation that gets students thinking about how molecules behave and react with their environment:

 

         What is a molecule made of? Answer: bonds and atoms with a particular arrangement in three-dimensional space

         What are molecules and what do they do? Encourage statements that molecules allow for chemical reactions to happen

         What do we call the way a molecule or substance reacts in a chemical reaction?      Answer: its chemical property

         What is it about a molecule that may cause a chemical reaction? Many answers are acceptable: atoms, where it is on the periodic table, its state of matter, its shape, the other molecules it is near

         Molecules behave according to their shape or the position of the atoms in a molecule. Let's imagine the following items are molecules. Who can describe to me what is special about these molecules?

o   keys

o   Screwdriver

o   Puzzle piece

o   Bowling Ball

Use the answers to conclude that a molecule's shape and its atoms helps determine what it can do and react with. In fact, how the atoms are positioned on a molecule is just as important as what the atoms are. Molecules can have the same molecular formula but behave differently or react differently. These types of molecules are called isomers.

 

 

 

Have the students use their hands as example to demonstrate this.

 

Organize the class into groups of 2-4. Using a washable marker, have two people in the group write A,B,C,D,E, on the tips of the fingers of both hands starting with the thumb. The letters and fingers represent the atoms of a molecule.

 

 

Have these two people sit opposite of each other. If one person puts up their left hand and the other person puts up their right hand, these two hands compare to each other perfectly.

Ask students:

  • What can you tell me about the fit of your hands?
  • Can you tell me how your left hand is different from your right?

 

With their hands properly labeled A through E, have the students investigate their hands. Try to put the hands together so that they align perfectly with each other (thumb to thumb, etc). Is it possible to do? So, even though these “molecules” have the same molecular formula and shape they are different.

 

Supply the students with a mirror and see if that helps them figure out how they differ. They share the same fingers or "atoms" yet are different. Explain and confirm to the students that your hands are just one example of isomers and a special situation: where how atoms are positioned on a molecule can make it seem the same, but be different in what it can do and react with.

 

Try this quick experiment to smell the two carvone isomers.  Procedure:

 

1.      Give each group a handful of caraway seeds and some mint leaves.

2.      In one bowl or plate, crush the caraway seeds; in the other bowl, crush up the mint leaves.

3.      Smell the crushed items from each sample and notice that the isomers have distinct smells.

Ask students:

  • Describe the smell of the two items. Do you think that these molecules are the same? Why or why not?
  • As an interactive conclusion to this experiment, have students see if they can figure out the similarity between the carvone molecule and fitting their right hand in a left-hand glove.
  • Show the students the molecule of carvone. This is what they have been smelling. Have students discover how they are the same and how they are different. Carvone has an isomer;  by examining the photo, they will notice that the molecules are mirror images of each other, just as their hands were, so one molecule is essentially left-handed (S) and the other is right-handed (R).

 

  • Note: the R and S designation is appointed to the way these two molecules react with polarized light.  For the purposes of this lesson, the designation of right and left are used to simplify the content for the middle school student.

 

Isomers of Carvone Molecule

(S) isomer "left-handed" is found in caraway seed

(R) isomer "right-handed" is found in spearmint

 

Both caraway and mint molecules look the same – but because they are mirror images, they are not exactly the same: they are isomers of carvone. The human nose has specific receptors for each kind of isomer. Imagine receptors in the nose shaped like gloves. Each isomer of carvone can only fit in the corresponding glove.

 

Finally, engage the students about careers or fields of science and technology where understanding isomers and the structure of molecules is important. In the field of medicine, for example, it is important to know if isomers of a drug exist: medicating people with mirror image isomers can have adverse effects on the human body.

 

Additional Resources:

         http://www.pbs.org/saf/1401/teaching/teachinghs.htm

         http://www.pbs.org/search/molecules/

         http://www.yteach.ie

Student Worksheet for: Molecules Shapes and Our World         

 

Name:______________________________________  Date: ________________

 

1. Fill in the missing term (see definitions):

        I.            A molecular formula tells the actual number of _______ in a molecule.

     II.            ________ are molecules that have the same atoms, but a different arrangement of their atoms.

2. Which of the following is an example of a mirror image isomer:

A. a ball                       B. a foot                  C. a drinking glass

 

3. How is your right hand different from the left?

 

_______________________________________________________________________

4. Why would knowing about isomers be important to a pharmacist?

 

_______________________________________________________________________

5. Besides the molecular formula of a compound, what else should a chemist know?

 

_______________________________________________________________________

Carvone Isomer Experiment

 

Experiment Title: ______________________Date: __________Name: ___________

 

Student Hypothesis: ___________________________________________________

 

Materials: __________________________________________________________

 

 

Procedure: __________________________________________________________

 

___________________________________________________________________

 

Observations:

___________________________________________________________________

 

___________________________________________________________________

 

 

Conclusion: __________________________________________________________

 

 

 

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