MOLECULAR HABITS; THEY'RE CRYSTAL CLEAR
Grades 5 - 7

We are so easily taken in by the beauty of large, dramatically faceted crystals that we tend to forget that the blueprint for this is found is found at the scale of the molecule. Through interactive demonstrations, hands on activities, and the incorporation of a 3-2-1 Classroom Contact video, this lesson will demonstrate two important properties of crystals; growth and habit.

"3-2-1 CLASSROOM CONTACT: Crystals, They're Habit Forming."

Students will be able to:

• describe the properties of growth and habit as pertaining to crystals.
• describe the relation of crystal size as a function of time.
• describe how the shape of the crystal comes from the shape of the molecules that make them up.

• One gallon plastic milk carton for every five students.
• Two, one pound container of salt.
• Three specimens, small, medium and large, of at least two different varieties of crystals. (Pyrite, Fluorite, Calcite, and Quartz make good examples and are relatively easy to acquire.
• One each of the following shapes cut from colored construction paper for every two children:
  • 2" x 2" square
  • 2" x 1" parallelogram
  • 2" x 1" rectangle
  • Diamond shapes with 2" x 1.5" axis
• Two sheets of drawing paper (12' x 24") per child.
• Pencil or pen and crayon for each student.
• One bamboo skewer for each child.
• Spool of clear nylon sewing thread or 4 to 6 lb. test monofilament fishing line.
• One metal screw or bolt per child.
• Masking tape.
• About 80 gumdrops, half green half orange.
• Two boxes of round or square \ round toothpicks.

Habit: The regular shape of crystals as determined by the structure of the molecules that make them up.
Crystallographer: One who studies crystals and the manner of their formation.
Cube: A regular solid body with six equal sides, all squares, and containing equal angels.
Mineral: Any ingredient in the Earth's crust. An inorganic body with a definite chemical composition.
Properties: A particular quality of anything; that which is inherent in a thing.
Molecule: The smallest unit of matter capable of existing independently while retaining its chemical properties.

Hold up the smallest example of the first variety of crystal (e.g. Pyrite?). " Does anybody know the name of this mineral and what we call these regular geometric shapes that we find minerals in.?"

Give the children the name of the mineral and the term "crystal" if they cannot provide it themselves. Hold up the same crystal. This is (pyrite).""

Hold up the medium size crystal."This is also pyrite. What is the difference between this crystal and the first one?" (size)

Hold up the large size crystal."This is a pyrite crystal as well. What is the difference between this crystal and the first two?" (size)

Go through the same procedure with the other crystal samples."We've seen crystals of the same type but in different sizes. Why do you think the crystals are different sizes and why do different minerals have crystals of different shapes?"

Write student responses on the board.

"We are now going to explore some of the properties of crystals and see if we can verify any of the answers you came up with or find some new or different solutions." To give students a specific responsibility for viewing, introduce the video by saying... "As you watch the first short segment of this video, observe and record what the young lady might be making and what materials she may be using. We will be duplicating her experiment at a later time."

Viewing Activities: Begin tape at the very beginning of the segment where the girl is emptying the contents of a plastic bag into a bowl of water.

Pause immediately after the girl says, "I'll get back to this later." Give students a moment to finish recording their observations.

Fast Forward tape through the 3-2-1 Contact promotional segment.

Pause when the screen displays the title, "They're Habit Forming -Crystals"

To give the students a specific responsibility while viewing say,"The young lady is now going show us a number of crystals that are both beautiful and interesting. As you view them, think of the different things which are made of crystals and if you know of any other kinds of crystals." RESUME Tape.

After the girl says, "Their are thousands of different kinds of crystals. Lots of things are made of crystals." PAUSE. "Do you know the names of any other kinds of crystals or the names of some things that are made of crystals?" Allow children time to respond.


"Next, we're going to find that there are some very special terms used by people who study crystals to describe their properties. In fact, we even have a special term to describe a person who studies crystals." To give students a specific responsibility while viewing say, "In the next segment of the video the young lady will reveal two things that all crystals have in common. I'd like you to record what those two common properties are and any special terms that are used to describe those properties. Also, if you were a person who studies crystals, take note of what you would be called." RESUME Tape.

To assess student comprehension and allow a discussion on the properties of crystals, PAUSE and MUTE the tape after the girl says, "They would say salt crystals, 'and those are salt crystals' have cube habits."

Discussion : - "What two properties do all crystals have in common?" - "What do we call a person who studies crystals?" - "What term do crystallographers use to describe the shape of crystals?" - "How many different kinds of crystals are there?" - "Do all crystals grow at the same speed?"

Stand to one side of the television screen and ask... "What kind of crystals are these?" (salt) "What kind of habit do they have? (cube) "Can anyone describe the properties of a cube?" Ask a student volunteer to come to the television with a dry erase marker and outline a salt crystal on the T.V. screen demonstrating its "cube" habit.

RESUME Tape until the next crystal appears on the television, then PAUSE. Ask another student volunteer to come to the television and outline the crystal in a way that will demonstrate its habit. Ask the class to think of a word that would describe the crystal's habit.

RESUME Tape until the third crystal type appears, then PAUSE. Continue the procedure as described above for crystal two.

RESUME Tape until the fourth crystal type appears, then PAUSE.

Repeat the procedure as above.

RESUME Tape until the fifth crystal type appears, then PAUSE. Repeat the procedures as for crystals one through four.

To give students a specific responsibility for viewing say, "We have seen that there are many types of crystals with many different habits. In the next segment of our video , look and listen to see if you can discover what is inside a crystal that gives it its particular shape or habit."

RESUME sound, RESUME Tape where the girl says, "This is a quartz crystal. It is made of millions, trillions of molecules."

PAUSE the tape after the girl finishes saying, " Of course crystals don't grow flat, they grow in all directions like this one, see. It grows this way, that way, all directions."

Discussion to test for comprehension: - "What is the smallest part that makes up a crystal?" (molecule) - "What effect does the shape of the molecules have on the final shape of the crystal?" - "Can molecules come together and attach themselves in any old way?"

To give the students a specific responsibility for viewing say... "We will now return to the young lady to see how the experiment she started in the beginning of the video is turning out. Observe and record any observations or changes in her experiment. If you can think of any explications for what is happening, please record that as well." RESUME Tape.

Immediately after the girl's opening statement, "Let's see how this is coming", press Mute. The girl will remove the crystals from the bowl. When the camera pans in for a close up of the crystals, PAUSE. Ask the students to record their observations. After giving the children a minute to record their observations, RESUME sound, RESUME Tape.


After the girl says, "I'll come back to this later, stick around", FAST FORWARD the tape through the second section of the tape which is on snow flake formation. FAST FORWARD through the outdoor scenes and photography. Continue to FAST FORWARD as the young lady enters a building and meets with two other children and a male adult. Shortly after the adult shakes hands with the girl he will display a ball and stick model of a crystal with a cube habit. When the screen focuses in on the crystalline model and the adult's hand points to its structure, press PLAY, then immediately PAUSE the tape.

To test the students for comprehension ask: "What habit does this crystal have? (cube). Would someone like to go to the T.V. screen with a pen and outline a section of the crystal which shows the smallest example of a cube?" (Have two more students come to the television and outline examples of smallest cube habits within the larger crystal).

Take out gumdrop and toothpick replica of the crystalline model on the video. Ask: "What do you think gives this large crystal its cube habit? " When students offer that it is the smaller structures with cube habits that make up the larger crystal, verify their correct answers by showing them a second gumdrop model. This second model (made of eight gumdrops and twelve toothpicks) represents the smallest structure with the cube habit. Point out that structures outlined by the students on the paused video image, and the second gumdrop model are the same. Ask the students if any of them might guess what the crystal with the cube habit on the video might be. (salt) If they cannot come up with the correct answer, tell them that its chemical name is sodium chloride and that they'd very likely find it on their dining room table at home.

Continue FAST FORWARD through the section on snowflakes. There will be several sections that will show snowflake growth and patterns. When the time lapse photography of snowflake formation suddenly changes to an image of rectangular and square crystals RESUME Tape at normal speed. There will be about a forty five second segment showing crystal formation. As soon as the young lady makes an appearance press STOP.

In order to make the previous concepts about crystal formation more concrete and to prepare students to form their own definitions of crystals say... "I am going to hand out one set of four patterns (square, diamond, rectangle and parallelogram), to every two students. These patterns represent the shapes or habits of four different molecules. First, place the square molecule pattern near the center of one sheet of your drawing paper and trace around it with your pencils. Next, by using the square crystal you just traced and by tracing around your molecule with the square habit three more times, I want you to make one large crystal with a square habit. Then use a crayon to outline your new four molecule crystal with the square habit. (Make sure that everyone has successfully drawn a four molecule crystal with a square habit.)

Next, I would like you to use the three other molecule shapes and make a four molecule crystal with the habit of the original molecules on your three remaining sheets of paper. When you are done, outline the shape of your new four molecule crystal. Check to see that everyone's work reflects understanding of the concept, (and the directions).

Once you have successfully completed all four of your four molecule crystals, make your crystals larger by tracing and adding more molecules. Assemble the largest molecule you can make on your sheet of paper and outline your final product with a crayon." To verify that everyone understands ask... "If your largest crystal is the correct shape, it should have the same habit as what?" (The original molecule )

When the children are done, ask them if they can give a definition of what a crystal is and how it gets its shape. Discuss the answers and see if they can come to a consensus on a single definition.

To give the students a specific responsibility for viewing say... "We are now going to hear from the young lady in the video again. She is going answer the same question I just asked you. "What is a crystal and how does it get its shape?" Let's see if her definition is anything like ours. Second, she is going to show us the conclusion of her experiment. Observe the results and think carefully about the question she asks us at the end."

RESUME Tape. After the girl says, "Can you imagine the shape of the molecules that make it up?" PAUSE the tape when the camera zooms in for a close up of her crystals.

Ask: "How did our students' definitions compare with the girl's? How did the crystals appear different from the first two times we saw the experiment? ,Why? How might what we saw with the young lady's experiment explain the different size crystals I showed you at the very beginning of this lesson?" What do you think the shape of the molecules that make up the crystals in the girl's experiment look like?"

If a student likes, let them go up and outline the crystalline shape on the T.V. screen.

To give the students a specific responsibility for viewing say... "The final segment of this video is a review of all the key ideas and illustrations we've seen so far. Look and listen carefully to what is pictured and said. Be sure that you share both questions and any observations you might have after this final part."

RESUME Tape. The final segment will end after the girl says, "Crystals have very regular habits." STOP Tape immediately. Provide question and share time.

We have watched crystals in the process of formation. We've studied their structure and habits. Now it is time for us to make our own crystals. Can anyone tell us what the girl in the video used to make her crystals ? (bowl, pencil, water, and probably sugar) Can anyone describe the process she used to make her crystals? (Have children explain the process as they saw and understood it)We will use a very similar process but will be making salt crystals instead."

1. Have students make crystal seed garden using kite string with a bolt or screw. See instruction sheet.

2. Have students fold a 4" piece of masking tape over the end of a bamboo skewer (the flat end) and write their name with water proof pen on it.

3. Fill glass jar (or plastic one gallon milk jug cut as shown on instruction sheet) with hot tap water super saturated with salt. If using milk jug, keep a plate, tray or other firm object under jug particularly when moving it. Allow students to observe salt crystals under some form of magnification.

4. Attach crystal seed garden to bamboo skewer using 4-6 lb. test monofilament fishing line. Length of line should let the seed garden (the metal screw ) hang one inch above the bottom of the jug. See instructions as to how skewer attaches to jug.

5. Once the solution has cooled, sprinkle a pinch of salt into the water over each suspended seed garden.

6. Ask the students what conditions would favor the largest crystal formation, rapid evaporation or slow evaporation, and have them explain why.

7. Move experiments to cool, dark place for a month of undisturbed crystal formation.

8. ASSESSMENT: Have students explain in terms of the concepts and vocabulary of the lesson how their crystals evolved. Having this occur three to four weeks after the actual lesson should be a good test of retention.

Have a geologist from either private industry or from a museum visit your class. A geologist can show , especially if they can include thin section slides and core samples, how crystal size can determine some of the history of the rock and the area it came from. A geologist from mining, petrochemical, or research oriented backgrounds can all relate how reading the rocks with their crystalline signatures aids in their work.

Social Studies \ Geography
Research the history of famous gems such as the Hope Diamond or the Crown Jewels of England. Research some of the great gem producing areas of the world . How has it impacted the history of those regions?

Math
Study and learn basic two dimensional geometric shapes. What next? Tetragonal dipyramid, Ditetragonal prism, Rhombic prism, Holy scalenohedron Batman! What three dimensional geometric shapes can be made by taping together two dimensional shapes?

Science
What minerals are actually found in the habits studied above? Where else are these shapes found in nature? What are the properties of Buckminster Fullerines?

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Resources:

Rocks and Minerals
Eyewitness Books
Dr. R.F. Symes
Alfred A. Knopf
New York

How Science Works
Readers Digest Association
Pleasantville, N.Y.

Adventures With Atoms And Molecules II
Robert C. Mebane, Thomas R. Rybolt
Enslow Publishers, Inc. N.J.

Collecting Rocks,Minerals, Gems and Fossils
Russell P. MacFall
Hawthorn Books, Inc. N. Y.

Guide To Rocks And Minerals
Mottana, Crespi, and Liborio
Simon and Schuster Inc. N.Y.

Peterson Guide To Rocks and Minerals
Frederick H. Pough
Houghton Mifflin Co., Boston

Treasures from the Earth: The World of Rocks and Minerals
Benjamin M. Shaub
Rutledge Books, Crown Publishers,Inc.
New York

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Master Teacher: Ralph Sodano

Click here to view the worksheet associated with this lesson.