Snowflake Science


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A brief overview of the science of snow.

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Snowflake Science

  1. 1. Chemistry S N O W F L A K E S Courtesy of Kenneth G. Libbrecht, Caltech
  2. 2. Ever Happened to You?
  3. 3. UGLY!!!
  4. 4. Snow can be beautiful…
  5. 5. A Closer Look at Snow…
  6. 6. What Are Snowflakes? <ul><li>Snowflakes are NOT frozen raindrops. </li></ul><ul><ul><li>Sometimes raindrops do freeze as they fall, but this is sleet . Sleet particles don't have any of the elaborate and symmetrical patterning found in snow crystals. </li></ul></ul>Snowflakes are crystals of H 2 O that form when conditions are right.
  7. 7. Formation of Snowflake Crystals???
  8. 8. Snowflakes form when water vapor condenses around a dust particle directly into ice, which happens in the clouds. The patterns emerge as the crystals grow. How Snowflakes Form
  9. 10. <ul><li>Water molecules in an ice crystal form a hexagonal lattice, as shown below: </li></ul><ul><ul><li>Red balls represent Oxygen </li></ul></ul><ul><ul><li>Grey sticks represent Hydrogen </li></ul></ul><ul><ul><li>Intermolecular forces between O’s & H’s link molecules </li></ul></ul>
  10. 11. How Big Do Snowflakes Get? The average snowflake measures around 1.2cm. You do need a magnifying glass to see the shape. Some of the largest snowflakes range from three to four inches in length!
  11. 12. So Many Shapes…How Can We Keep Them All Straight?
  12. 13. Systems for Classifying <ul><li>International Classification System </li></ul><ul><ul><li>Simple but widely used </li></ul></ul><ul><ul><li>Seven main types </li></ul></ul><ul><li>Ukichiro Nakaya </li></ul><ul><ul><li>41 distinct types </li></ul></ul><ul><li>Magono and Lee </li></ul><ul><ul><li>Most complex </li></ul></ul><ul><ul><li>80 types </li></ul></ul>
  13. 14. Morphology Diagram
  14. 15. Simple Prisms <ul><li>Hexagonal </li></ul><ul><li>Solid “faces” </li></ul><ul><li>Glass-pane look </li></ul>
  15. 16. Hollow Column <ul><li>Cone-shaped hollow regions at ends </li></ul><ul><li>Hexagonal column </li></ul><ul><li>Very small, relatively </li></ul>
  16. 17. Stellar Plates <ul><li>Form near -2 ° C or near -15 ° C </li></ul><ul><li>Six broad arms </li></ul><ul><li>Star-like shape </li></ul>
  17. 18. Stellar Dendrites <ul><li>Plate-like basic shape </li></ul><ul><li>“ Tree-like” branches and sub-brances </li></ul><ul><li>Fairly large </li></ul><ul><ul><li>Easily seen with naked eye </li></ul></ul>
  18. 19. 12-Sided <ul><li>Two stellar-dendrites grown together </li></ul><ul><li>Rotated 30 ° </li></ul><ul><li>Very rare </li></ul>
  19. 20. How Does Knowledge of Snowflakes Apply to Life? <ul><li>Ski slopes sometimes need to make their own snow </li></ul><ul><li>The entire computer industry rests on silicon and other semiconductor crystals </li></ul><ul><ul><li>We don't know much about how these crystals form </li></ul></ul><ul><ul><li>Maybe similar to snowflakes </li></ul></ul><ul><li>Knowledge is never useless! </li></ul>
  20. 21. Growing Snow in a Lab??? Vapor diffusion chamber - an insulated box that is kept cold on the bottom (-40 ° C) and hot on the top (+40°C).  A source of water is placed at the top, and water vapor diffuses down through the box, producing supersaturated air.   The cold, supersaturated air at the center of the chamber is ideal for growing ice crystals.
  21. 22. Basil Mason’s Electric Wire <ul><li>Putting a wire into the diffusion chamber and then applying a high voltage to the wire, slender snow crystals begin growing from the wire. </li></ul><ul><ul><li>Since water molecules have an intrinsic electric polarizability, the electric fields tend to polarize the water molecules. </li></ul></ul><ul><ul><ul><li>The electric effects come about because electric fields influence the way water molecules diffuse through the air in the vicinity of the ice surface. </li></ul></ul></ul>wire crystal
  22. 23. Better Snowflakes Through <ul><li>The best electric needle snowflakes grow only when certain chemical vapors are added to the diffusion chamber. </li></ul><ul><ul><li>Silicon caulk vapor </li></ul></ul><ul><ul><li>Acetic acid vapor </li></ul></ul><ul><ul><li>Gasoline vapor </li></ul></ul>Chemistry
  23. 24. Artificial Snow <ul><li>Snow machines shoot a mixture of water and compressed air out of nozzles. The water comes out as fine droplets, and the air cools as it decompresses, causing the droplets to freeze. A fan blows the ice particles onto the slopes. </li></ul><ul><li>You can see from the picture at left that artificial snow is made of frozen water droplets, with none of the elaborate structure found in real snow crystals. </li></ul>
  24. 25. This has been a presentation of Gary G. Abud, Jr.