Water
The Amazing Water Molecule
Top: Clouds, fog, and mist are a cluster of tiny liquid water droplets called drizzle drops.  Bottom: Snowflakes are ice crystals. Temperature and humidity determine their shapes.

Water may not seem special. It's clear. It has no taste. It doesn't smell like anything. But if it couldn't do the things it does, life on Earth would not exist.

Water is a tiny molecule. It consists of three atoms: two of hydrogen and one of oxygen. Water molecules cling to each other because of a force called hydrogen bonding. It's the reason why water can do amazing things.

Water is a shape-shifter. It exists in three states on Earth: liquid, gas, and solid:

  • Liquid water is a jumbled bunch of water molecules. It comes out of our faucets, flows underground and in rivers and oceans, and forms clouds and fog in the air.
  • When water molecules escape from liquid water and float into the air, they turn into an invisible gas called water vapor. The spaces between the molecules are much bigger than the molecules themselves.
  • When water freezes into a solid, it does a strange thing: it floats! (Most other solids become denser and sink.) As ice forms, water molecules arrange themselves neatly in a crystal structure. The empty spaces between the molecules act as flotation devices—the way a life preserver holds you up.
 
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