Academic standards correlations on Teachers' Domain use the Achievement Standards Network (ASN) database of state and national standards, provided to NSDL projects courtesy of JES & Co.
We assign reference terms to each statement within a standards document and to each media resource, and correlations are based upon matches of these terms for a given grade band. If a particular standards document of interest to you is not displayed yet, it most likely has not yet been processed by ASN or by Teachers' Domain. We will be adding social studies and arts correlations over the coming year, and also will be increasing the specificity of alignment.
Are all snowflakes truly unique? What are the physical forces that drive snowflakes to come in so many shapes and sizes? In this lesson, students build an apparatus that creates conditions similar to a winter cloud and produce their own snow crystals indoors. By watching the snow crystals grow, they learn about the molecular forces that shape ice crystals, and gain a deeper understanding of the states of matter. By exploring media resources, including microphotographs of real snowflakes, students also learn about molecular forces, the particulate nature of matter, and condensation.
Snowflake Photo Gallery PDF Document
Instructions for Growing Your Own Snow Crystals PDF Document
Snow Crystal Growth in Detail PDF Document
Snow Morphology Diagram PDF Document
A Guide to Snowflakes PDF Document
1. Tell students that they will begin by viewing microphotographs of real snowflakes collected from different parts of North America. Divide the class into pairs or small groups, and have each group view the Snowflake Photo Gallery PDF Document. How many different kinds of snowflakes can they see? Do they observe any patterns?
2. Show students "Types of Snowflakes" in the Snowflake Physics Flash Interactive and ask them how they might classify the snowflakes they described earlier. Then ask students to hypothesize in their notebooks about how the different kinds of snowflakes form, including the most familiar kind, the six-sided, feathery shaped ones. You may want to ask students to draw the different stages in the development of a snowflake. When they are finished, ask them if they have ever had the chance to look at real snowflakes. Did any of them look like these?
3. Bring the class together to discuss what they've found. Most students will have noticed that many snowflakes are six-sided. Ask them if that seems to be universally true. Are there any cubical or tetrahedral snowflakes? Some students may notice that a few of the snowflakes look like feathers, cylinders, or spindles. Make note of this on the board as it will come up again later in the lesson.
4. Tell students that they will now have the opportunity to watch snowflakes forming in the laboratory. Show "Watch a Snowflake Grow" in the Snowflake Physics Flash Interactive to present actual evidence of how snowflakes form. Discuss the following questions to encourage students to think about how the conditions under which snowflakes grow can affect the outcome of their structure.
5. [Optional] Using a number of physical stick models, demonstrate the 109° angle of water molecules. Show how these can be built into a hexagon. Then have students build their own hexagons. Ask them to arrange their hexagons in different patterns that might suggest how snowflakes are formed. They can stack them and make towers, or combine them edge to edge. Once they've explored this for a while, have them view the snowflakes again and compare their ideas about snowflake formation with what they have observed. Finally, they can read the "Snowflake Basics" text in the Snowflake Physics Flash Interactive.
6. Tell students that they will now build a diffusion chamber—an apparatus that grows snowflakes. Distribute the Instructions for Growing Your Own Snow Crystals PDF Document, then have students work in pairs or small groups to create their chambers. To save time, make sure the materials are available in a central location.
7. As the snowflakes grow in the diffusion chamber, each student should make a sketch of their growing snowflakes every three minutes. One factor to note is how far down the nylon line the snowflakes are located. Encourage students to try to draw the nylon line to scale and to show all the colonies of snowflakes that are growing at different locations along the line. This time-lapse series of drawings will be used in the follow-up discussion. Remind students that the snowflakes are fragile, and that a slight tap on the bottle might dislodge them.
8. Bring the class back together so that students can share their results. Start the discussion by asking if anyone noticed hexagonal shapes or the traditional 109–120° angles. They may have to look carefully to see these, as the results are often a feathery frost, or "fuzz." Encourage them to look closely. Even students whose snowflakes did not grow to be perfectly formed will have their results validated when they see that the principles followed by the water vapor molecules as they condense hold true whether their result is needles (dendrites), traditional snowflakes, or even the fishbone pattern. Try to elicit student theories about why some of their results differed while others were the same. For example, students may have noticed that the largest flakes tended to grow at the same location on the string for each group—right above the top of the cardboard cover, where the cold air in the bottom meets the warm humid air at the top.
You might want to point out how sensitive the crystals are to the conditions of humidity and temperature under which they are formed. Even a slight difference of a few degrees will greatly alter the size and structure of the crystals. Inside the diffusion chambers, there is a gradient of temperature (warm at the top, cold at the bottom).
Inside clouds, there is also a temperature gradient. As the supersaturated air moves about inside the clouds, the growing ice crystals are subjected to different conditions. As they tumble and fall through the clouds, no snowflake follows exactly the same trajectory, nor does it experience the same conditions as any other. Thus, on the microscopic level, every snowflake is indeed different.
9. At this point, many students will be ready to explore in detail some of the physics behind snowflakes. Show students the Snow Morphology Diagram PDF Document. You may need to explain this diagram, starting with the meaning of the two axes. Temperature, along the bottom axis, varies due to weather conditions and height above Earth’s surface (generally the higher the altitude, the colder it is). Saturation can vary within a cloud based on the mixing of different air masses along a frontal system. Based on this diagram, ask students to discuss under what conditions of temperature and saturation their snow crystals would have formed if they had been formed naturally in a cloud. What could they do to their apparatus if they wanted to try to grow a different type of snowflake?
Select one of the following activities for all students to complete, or assign each activity to half of the class: