Tuesday, 24 December 2013

Snowflake science: the structure of ice

snowflake photos by Wilson Bentley
 If I've learnt anything from chemistry, it's this: water is amazing. Before, I've talked about it in the cohesion-tension theory in which plants use its polarity to draw it up from the ground, but since it's winter, I'm going to try to explain why snowflakes are six-sided.

A water molecule is made up of two hydrogen atoms attached to one oxygen atom. The hydrogens repel to get as far away as possible from each other, but because of the configuration of the electrons around the oxygen, a water molecule isn't just a straight line.

water molecule from Chemical Forums
The crosses and dots represent electrons. The pairs of electrons are all negative,
so repel to get as far away as possible from each other.
The water molecule is what we call a 'bent' or 'V-shaped' molecule, and the angle between the two hydrogens is a bit less than 109°, the angle inside a tetrahedron.

Water molecules can form hydrogen bonds between themselves, which accounts for many of the characteristics of water. A hydrogen is attracted to the lone pair of electrons on the oxygen of a different molecule. One water molecule can form hydrogen bonds with four other molecules to form that crucial tetrahedral shape. Together, the molecules of water in ice form a tetrahedral structure.

structure of ice from 800 Main Street
Can you see the hexagon in the image above? Because of these hexagons that appear in the atomic scale, resulting snowflakes are six-sided.

To fold a scientifically correct snowflake, once you've folded your circle of paper in half,
instead of folding it in half again, fold it into thirds.
 If you want to know more about water - its lower density in solid form, surface tension, slipperiness - have a look at this gentle introduction.

Merry Christmas!

1 comment:

  1. great post! would you like to follow eachother?


Thank you ♥

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