BACKGROUND:
Water is a transparent, odorless,
tasteless liquid composed of the elements hydrogen and oxygen. It is a
very good solvent, meaning that many substances can dissolve in it easily.
Water is important to our lives, and without it we could not live.
In fact, there are no living creatures that can live without water.
There are four states of matter commonly found
in the Universe. There are solids, liquid, gases, and plasma.
There is also a fifth state of matter, the Bose-Einstein Condensate which
is seen at extremely low temperatures. All matter is found in these states.
Water is one of the few substances that can easily change into three of
the states, liquid, gas, and solid. Water goes through three states of
matter easily. Ice is when water is solid, steam is when water is gas, and water usually refers to its liquid state.
Water illustrates the three states of matter: solid (ice),
gas (steam), and liquid (water). The form it takes depends upon the
temperature. At low temperatures, the molecules do not move around
as much and form a crystalline structure that is rigid (ice). In
the liquid state, water molecules move more freely. Water molecules
in the form of steam are moving very fast with large spaces between the
molecules. Although ice is crystalline, it tends to have the molecules
in a rigid structure that is spaced farther than the molecules of liquid
water and this is quite important, for if ice were denser, it would sink
in water. Imagine what would happen if icebergs grew from the bottom
of the ocean instead of floating on the surface.
PROCEDURE:
- Water is a unique substance.
Hold up a glass of water to your class. Ask students what is in the
plastic glass, and how do they know. Ask them if they have seen water
in other forms. Hopefully some of your students will know that ice
and steam are other forms of water. Water can take on 3 states of
matter, liquid, solid, or gas.
- Give students a small cup of water
and see if they can determine what state of matter is water at room temperature.
Have them touch the water, drink it, smell it, and listen to it.
Do this very slowly, emphasizing the characteristics of water.
- Students should become acquainted
with the properties of a liquid. A liquid can be more than just water.
Discuss with your students that even substances like a rock can become
melted and act like a liquid. Wetness or coldness does not
characterize all liquids. The key property of a liquid is that it
flows when poured.
- On the worksheet there are several
forms that water takes in nature. Snow and hail is a solid, sleet
has solids within a liquid mass, and rain is liquid. Ask students
if they can find the gas phase of water. They may not recognize that
a cloud contains components of water in the gas phase. Clouds also
have particles in it, which are in the solid phase.
- If students are unfamiliar with these
type of weather phenomena, you may want to go over each type. Hail
is frozen water that moves up and down in clouds, so it freezes as it is
moving, giving it the spherical shape. Snow is water that crystallizes
when the temperature gets below freezing. Sleet is when the temperature
freezes, but then as it falls from the clouds it partially melts.
Clouds actually contain 2 states of matter, solid and gas. Rain is liquid.
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