TEACHER'S NOTES
SEEING IS BELIEVING
Atoms and molecules were first "observed" through the use of indirect evidence. The kids can have a chance to do this for objects much larger than atoms. This activity can also reinforce the idea of an object's properties and encourage kids to identify properties beyond the obvious ones they can see. Encourage the kids to use all of their senses. And get them to focus on the properties and to use them to justify their guess; they would prefer to guess right away. Don't open the containers; scientists can't check to see if they got the "right" answer.
AIR ATOMS
The vibrating can causes the atoms (molecules) in the air to move which, in turn, cause the (atoms in the) plastic to move. It is this motion that cause the salt to bounce. The motion of the air molecules also directly affects the salt but is too small to see. The elasticity of the tightly stretched plastic amplifies the movement so we can see it. If there were no molecules in the air, there would be no connection between the can and the salt so the salt would not move.
MAKING MOLECULES
How do atoms and molecules relate to each other? Molecules are made of atoms. Different combinations of atoms make different molecules. And molecules can be mixed together to get different substances. This exercise lets the kids build some simple molecules from atoms and lets them make "salt water" and "carbonated salt water". The atoms are made of gum drops, mini-marshmellos, or jelly beans. Since you may choose to let the kids eat the molecules when they're done, provide enough for each child to work alone. Before you start, figure out what color will represent what element and have the kids record this in the table under "Materials". In addition to 9 toothpicks per child (250 per class), you will need:
| Element | Per Child | Per Class |
| H | 5 | 125 |
| O | 4 | 100 |
| C | 2 | 50 |
| Na | 1 | 25 |
| Cl | 1 | 25 |
| N | 1 | 25 |
MOVING MOLECULES
Even though an object, in this case a quantity of liquid, appears to be still, its atoms and molecules are constantly in motion. We can demonstrate this by adding food color to "still" water. If the water were truly still, the food color might sink to the bottom due to gravity, but then it would just sit there. It's the molecular motion that causes the food color molecules to be distributed among the water molecules. Since the motion of molecules increases with heat, the food color should spread faster in warm water and slower in cold water.
COLD FACTS
Aside from exploring the relationship among the different phases of matter, this activity provides exposure to the concept of volume and its relation to height. Also, the kids get an opportunity to make accurate measurements (in your choice of English or metric units).
Looking at the change in volume between the solid and liquid phases is safer that looking at the gas phase since water must be heated to boiling to change to gas. The water level should fall as the ice melts. It is important that the ice cubes are floating. If there is too much ice or not enough water so that the cubes do not float, the water level will rise as the ice melts. The last question is a "trick" question since a fixed amount of matter is the gas phase does not have a unique volume. The gas will expand to fill its container so its volume is determined by that container.
THE POWER OF ICE
This is an opportunity to do a science experiment at home. The lid of the container will get pushed off as the water freezes because the force of the expansion that occurs as the water freezes is very strong. NEVER do this with a glass jar since the glass will break.
A CHEMICAL CURIOSITY
Here the kids will be able to observe a dramatic example of a chemical change (reaction) in which baking soda reacts with vinegar to create, among other things, carbon dioxide (the gas in soda). Since carbon dioxide is a gas, it will try to expand and therefore expand the plastic bag. If you add enough of the reagents, you'll make so much gas that the bag will burst open. Safety glasses are recommended more for form that out of necessity. It is unlikely that anyone will get vinegar in their eyes.
DANCING RAISINS
This experiment mentions the "weight" of the raisin. Actually, the property in effect is buoyancy - the ability to float. In its natural state, raisins are not buoyant. After several minutes in a carbonated beverage, the raisins will start to "dance". While they are sitting on the bottom, you can see gas bubbles start to collect on them. When there is sufficient amount of gas to make the raisins buoyant, they will rise. At the surface, some of the gas bubbles are exposed to the air and diffuse into the air. Once a sufficient number have "popped", the raisin is no longer buoyant and will sink.