What is water?
All matter is made up of atoms. Atoms join together to make molecules. A water molecule is composed of 2 hydrogen atoms and 1 oxygen atom.

What holds water together?
Water molecules are polar - that is each molecule has a positive electrical charge on one end and a negative electrical charge on the other end. Because opposite charges attract one another, the positive end of one water molecule attracts the negative end of another molecule. In this way, water molecules are held together.

Look at a hanging drop of water on Michael's finger!

Some New Terms:

Water & Oil
Some molecules are not polar - that is they don't have a positive or a negative end. They don't have a pole for a water molecule to become attracted to. Thus, oil molecules do not attract water molecules and will not mix if poured together.
They will separate into two different layers if left still for a period of time.

When working with liquids, you can easily observe differences in density when you pour the same amount of different liquids into a beaker. The liquids with the lower density will float on top of the liquids with a heavier density.

Liquids are unique! When poured slowly, they will spread out into a pool. Liquids need a container to contain them & they take the shape of the container they are poured into. Different liquids have a unique "feel" -- some feel oily, greasy, sticky or wet.

Surface Tension
Liquids have their own special properties. One is surface tension. The molecules in the top layer of a liquid are attracted to the ones beside and BELOW them. Because there are many molecules BELOW the top layer of molecules in a liquid and no molecules above the top layer, the top layer of molecules are pulled strongly downward. This makes the liquid act as if it has an elastic skin. Different liquids have different strengths of surface tension. This same property also causes liquid droplets to have different shapes depending on the type of liquid.

Look at these water droplets resting on wax paper . . .

Capillary Action
Liquids can move into very small spaces like a thin, thin tube. The molecules of a liquid are drawn into a thin tube by the force of capillary action. How does capillary action work?
Remember that molecules are attracted to one another so where one molecule goes, another will follow and another, and another, and another . . . . All the molecules are "pulled along" because of their polar attraction to each other.
An example of this occurs in plants where the water moves through the stem from the roots. Another example is when you place a corner of a piece of paper towel into a coloured liquid. The liquid will spread into the paper towel from the corner!
It is interesting to note that the narrower the tube, the farther the liquid molecules will move.

If you can make a material with pores (little holes) that are small enough, the water molecules will NOT be able to pass through and the material is water-repellent or water-proof.

You can pour liquids. How? There is very little resistance between the molecules in a liquid and they can easily move overtop, underneith and around each other. Some liquids pour more easily than others. Have you noticed this?
Honey, for instance, pours much more slowly than maple syrup. Maple syrup pours more slowly than water.
If the friction or resistance between the molecules is great, the liquid will poor slowly. In this case, it has a very HIGH viscosity. If the friction or resistance between the molecules is low, the liquid will poor quickly. In this case, it has a very LOW viscosity. Honey has a higher viscosity than maple syrup which, in turn, has a higher viscosity than water.

Some liquids are great solvents: they can easily allow other substances to dissolve within them. Certain liquids contain molecules with very strong poles - that is their opposite ends have strong electrical charges. These strong poles hold other liquids in "solution". A "solution" will not separate (settle out) into different layers as in a "suspension". In a suspension the polar attraction between molecules is weak, therefore, the molecules will break apart and settle out into their different component substance layers (due to differences in density between substances).

Gas into Water - Water into Ice
Water is the only liquid that can easily change state. That is, it can be changed from a liquid into a gas or a liquid into a solid by either heating or cooling (as in "melting").
In a solid state (ice), water molecules are held are close together and cannot change positon. The molecules ARE slightly vibrating though!
In a gaseous state (steam), water molecules are able to fill a very large space, move far apart and are constantly moving and changing positon relative to each other.
In a liquid state (water), water molecules are able to change position relative to one another but are held in relative proximity ('closeness').
To change the state of water, you must either add or subtract heat (cool).

Return to Grade 2 Science Home Page