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6.2: States of Water

Difficulty Level: Basic / At Grade Created by: CK-12
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What are the three states of water in this photo?

Water is present as liquid, solid and gas in this photo. We take water for granted here on Earth because there is a lot of it!

The Water Molecule

A molecule of water (See the Figure below) is made of three atoms bonded together. Two of these atoms are hydrogen and one atom is oxygen. The hydrogen ions have a positive electrical charge. The oxygen atom has a negative electrical charge. The hydrogen atoms are located on one side and the oxygen atom on the other. This means that the side with the hydrogen ions has a slightly positive charge. The other side, the side without the hydrogen ions, has a slightly negative charge. The water molecule is a polar molecule.

A water molecule. The side with the hydrogen atoms has a slightly positive charge. The side with the oxygen atom has a slightly negative charge.

Water has remarkable properties. Water expands when it freezes, even though all other substances contract. This means that in the winter ice on a pond or lake will float. Water has high surface tension because polar molecules tend to stick together. That's why drops stick together or some bugs can walk on the surface of a pond. Without water, life might not be able to exist on Earth. If it did exist it would not be as diverse or as complex.

Three States of Matter

Water is the only substance on Earth that is present in all three states of matter. This means that water is present as a solid, liquid and gas. Earth is the only planet where water is present in all three states. All three phases may be present in a single location or in a region. The three phases are solid (ice or snow), liquid (water), and gas (water vapor). See ice, water, and clouds (Figure below).

(A) Ice floating in the sea. Can you find all three phases of water in this image? (B) Liquid water. (C) Water vapor is invisible, but clouds that form when water vapor condenses are not.

Vocabulary

  • polar molecule: A molecule with an unevenly distributed electrical charge.
  • water vapor: Water in the form of a gas. Water vapor is invisible to humans; when we see clouds, we actually are seeing liquid water in the clouds.

Summary

  • Water is a polar molecule. One one side there is a positive electrical charge. On the other side there is a negative charge.
  • Water is the only substance on Earth that is stable in all three states.
  • Earth is the only planet in the Solar System that has water in all three states.

Practice

Use this resource to answer the questions that follow.

States of Matter at http://www.youtube.com/watch?v=KCL8zqjXbME (4:53)

  1. What is water made of?
  2. Explain how water becomes a solid.
  3. What happens when a solid melts?
  4. How do molecules move in a liquid?
  5. What are the major differences between a solid, a liquid, and a ga

Review

  1. What is a polar molecule?
  2. What are the three states of matter?
  3. What are some of the remarkable properties of water?

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Description

Difficulty Level:

Basic

Grades:

6 , 7 , 8

Date Created:

Jan 04, 2013

Last Modified:

Jan 07, 2014
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