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  • Chemistry is in everything, including snow.

  • Crystallography allows us to study the arrangement of atoms

  • in a snowflake crystal.

  • Though they all pretty much start the same, once they begin crystallizing,

  • it's true that no two snow flakes are alike.

  • And the number of possible shapes is staggering.

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  • A snowflake starts as a dust grain floating in a cloud. Water vapor in the

  • air sticks to the dust grain and the resulting droplet turns directly into ice.

  • Crystal faces appear on the frozen droplet.

  • Then, a prism forms with six faces and a top and bottom.

  • A cavity forms in each prism face because ice grows fastest near the edges.

  • Faster growth on the corners causes six branches to sprout.

  • The lines in each branch are due to ridges and grooves on the surface.

  • These six branches form the corners of a hexagon, which occurs because the water

  • molecules chemically bond into a hexagonal network.

  • When the temperature cools to -13 degrees C (9F), new

  • growth at the branch tips narrows.

  • At -14 degrees (6F), side branches sprout on each branch.

  • Suddenly, the crystal encounters a quick blast of warmer air followed by cooler

  • air, and more side branches sprout.

  • The crystal gradually warms, making the tips long and narrow.

  • The crystal encounters into even warmer air, which slows

  • the growth and widens the tips.

  • Finally, this unique and delicate structure falls to the earth along

  • with countless other snowflakes.

  • Cool, right?

  • Over the years, crystallographers have been classifying snow crystals into

  • different categories based on their arrangement of atoms

  • (column, plane, aggregation, rimmed, germs, irregular, other).

  • In the 1930s, there were 21 different classifications of snowflake could be in,

  • but by 2013 that number has soared to 121 categories.

  • To see the snow crystals at the molecular level, scientists send a beam of

  • x-rays through a samples of snowflakes.

  • The X-rays bounce off all the atoms in the snowflake and head in all

  • different directions, sort of like light off all the sides of a disco ball.

  • By seeing where these beams end up, we can figure out what arrangement

  • the snowflake's atoms are in, and therefore what it looks like at the atomic level.

  • Who's to say what new snowflake categories crystallographers will find in 2016.

  • But one thing's for certain, the ever-changing environment means that snowflakes

  • can have a mind-boggling array of shapes.

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Chemistry is in everything, including snow.

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B2 US snowflake arrangement branch droplet prism air

How Do Snowflakes Form?

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    大菲鴨阿 posted on 2019/01/11
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