A molecule is the smallest possible amount of a substance that can still be identified as that substance. For example, a molecule of water is the smallest droplet of water that is still water. If a molecule is broken down further, it becomes the atoms that create the substance. An atom is the smallest particle of a substance that can exist by itself.
So, a water molecule consists of two atoms of hydrogen and one atom of oxygen. This creates the chemical formula for water H2O. A water molecule broken down to its atoms is no longer water, instead it is atoms.
Molecules in Solids, Liquids, and Gases
Molecules that are close together and slow-moving create solids, which hold their shape. As molecules move away from one another (say, from being heated), a flowing liquid is formed. Add more heat, or energy, and the molecules spread out even more, creating a gas. Drop an ice cube on a hot frying pan to watch water molecules move through all three phases.
Water Molecules in Motion
Although kids can’t see molecules, this simple experiment shows kids how molecules move at different speeds depending on the temperature. Get two clear glasses or jars. Fill one with ice water (scoop out the ice after the water is chilled) and one with hot water. Add a few drops of food coloring to both glasses. Don’t stir the water or move the glasses.
Because the molecules in the hot water move fast, the food coloring will disperse through the water more quickly than it will through the slower-moving molecules in the cold water. Check the glasses every ten-to-twenty minutes to observe how the molecules move the color throughout the glass.
Spaces Between Molecules
There are spaces between water molecules, allowing other things, like salt and sugar molecules to fit between the water molecules. This experiment shows how other substances can fit between water molecules – without changing the level of water in a glass.
Pour one-cup of water into a two-cup measuring cup. Pour in a teaspoon of salt and stir until the salt dissolves. Pour in another teaspoon of salt and stir some more. Continue adding salt and stirring until the salt stops dissolving (the crystals will settle to the bottom of the cup). Check the water level – did the addition of the salt change the level? Rinse the cup.
Add one-cup of cold water into a two-cup glass measuring cup. Pour in a teaspoon of sugar and stir. Continue adding sugar, a teaspoon at a time, but this time stop when the water level changes. Now, heat the sugar water in a microwave for 30 seconds to one minute. Check if the water level went down. Add another teaspoon of sugar. When the water level goes up, heat the water. How many more teaspoons of sugar can be added to hot water than cold water? Because the hot water molecules are further apart than the cold water molecules, the hot water can hold more sugar.
Homeschoolers (and their parents) can do these simple experiments that show them how molecules move and how there are spaces between molecules. Continue the exploration of molecules with density, solutions, and super saturated sugar solutions.