CHEMISTRY NOW: Molecules, Isomers and Our World (Grades 5-8)
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
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.
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
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
Pair of gloves
Mint leaves (fresh or dried)
2 small bowls and 2 spoons per group of 4-5
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 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.
- • 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.
- • 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.
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: ___________________________________________________