Water and Its Properties Mrs. Labuhn – Science 6 th Grade

Background Water is an essential part of the earth system. It covers over 70% of the earth's surface. It is the only known substance that can exist in gaseous, liquid, and solid phases within the relatively narrow range of temperatures and pressures found on earth.

Water’s Molecular Structure Water's special qualities come from the unique shape of the water molecule. Each molecule contains two atoms of hydrogen and one atom of oxygen. In general, when considering the states of matter, solids are more dense than liquids and liquids are more dense than gases.

Solid State (Ice) The water molecules are packed close together preventing it from changing shape. Ice has a very regular pattern with the molecules rigidly apart from one another connected by the hydrogen bonds that form a crystalline lattice. These crystals have a number of open regions and pockets making ice less dense than liquid water. This is why ice floats on water. Ice forms when the temperature is below freezing (0°Celsius or 32°Fahrenheit).

Solid State Structure

Liquid State (Water) The attractive forces between molecules weaken and individual molecules can begin to move around each other. Because the molecules can slip and slide around one another, water takes the shape of any container it is in.

Liquid Water Structure

Gaseous State (Water Vapor) Water molecules move very rapidly and are not bound together. We cannot see water in its gaseous state, we can feel it in the air on a hot, humid day. Commonly, water boils at a temperature of 100°C or 212°F, forming water vapor. Many people believe that the visible plume of steam from a boiling kettle is water vapor. However, the steam that you see consists of very small water droplets suspended in the air, while water vapor is the invisible gas that results when water evaporates.

Gaseous State Structure

Water Cycle Water cycles endlessly throughout the atmosphere, oceans, land, and life of planet earth, taking each physical state at one time or another.

Universal Solvent Water is called the "universal solvent" because it can dissolve more elements than any other liquid. When water is free of all impurities, it has a neutral pH reading of 7, indicating that it is neither basic nor acidic, which is the reason that it is so effective as a solvent.

Adhesion and Cohesion Water is attracted to other water Cohesion. Water is attracted to other material Adhesion.

Importance of Water Water is important for: Agriculture Power Generation Public Health Protecting and maintaining water resources

Surface Tension is the name we give to the cohesion of water molecules at the surface of a body of water. Water is not attracted to wax paper (there is no adhesion between the drop and the wax paper). Each molecule in the water drop is attracted to the other water molecules in the drop. This causes the water to pull itself into a shape with the smallest amount of surface area, a bead (sphere). All the water molecules on the surface of the bead are 'holding' each other together or creating surface tension.

Capillary Action Surface tension is related to the cohesive properties of water. Capillary action however, is related to the adhesive properties of water. You can see capillary action 'in action' by placing a straw into a glass of water. The water 'climbs' up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to a the straw molecules the other water molecules also move up into the straw. Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water.

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