Water is the most abundant chemical compound on earth. Water covers three-fourths of the planet's surface. Polar ice caps contain most of the world's fresh water in the form of ice and snow. After nitrogen and oxygen, water is the third most abundant substance in the earth's atmosphere.

Yet, as common as water is, it is one of the strangest chemicals known. Unlike most other liquids, water flows faster under high pressure than under low pressure. Ice is unusual because it floats on liquid water. (The solid form of most other substances is more dense than the liquid form.) Unlike most other solids, ice melts under pressure. The melting and boiling points of water are unusually high for its molar mass. Water's uncommonly high specific heat helps to keep the planet warm and its high heat of vaporization stores solar energy that is released in storms.

In this Internet activity you will explore properties of water in its three states: solid, liquid, and gas.

1. Go to Water Science for Schools at the United States Geological Survey Web site, answer Challenge Question #3, check your answers, and read the explanations.
   
   
2. What are some chemical compounds contained in acid rain?
   
   
3. Why are raindrops shaped the way they are?
   
   

Additional Activities

1. Read Wet, Wild and Weird, a Discover magazine article on the strangeness and simplicity of water, and find at least three unusual properties of water.
   
   
2. Which freezes faster, hot water or cold water? Find out at The Straight Dope.
   
   
3. Have you ever wondered how much of your state is under water? Find out at the USGS Water Science for Schools site.