Next week we begin our second unit of the year: Chemical Reactions and Matter — “How Can We Make Something New That Was Not There Before?
This unit begins with an everyday mystery: what happens when a bath bomb is dropped into water? Students watch as it fizzes, breaks apart, and releases gas bubbles. They share and compare their ideas about where the gas comes from—some think it was trapped inside the bath bomb, others think it must have formed during the reaction. These initial ideas set the stage for a series of investigations that help students test their explanations and refine their models.
Next, students measure changes in mass in both closed and open systems to see if the gas was already in the bath bomb or made during the process. Once they establish that the gas must come from changes to the substances themselves, they turn to the ingredients of a bath bomb, testing each one in water. None produce bubbles alone, so students begin combining them in different ways to see what happens. When only certain mixtures create gas, students realize that something new may be forming. They then collect data on the properties of the gas—such as whether it rises or sinks, and whether it puts out or feeds a flame—to narrow down what kind of gas it could be.
In the next stage, students apply what they’ve learned to another reaction called Elephant’s Toothpaste, analyzing how properties can reveal when a new substance is produced. They then take stock of all their evidence so far, revising their class model to show how matter that goes into a system can differ from what comes out. This raises a new question: if something new was made, where did its particles come from?
Students move to a smaller scale, exploring whether new particles can actually be made from old ones. They test this by adding energy to water in two ways—first through heat, then through electricity—and compare what happens. These experiments lead to a discussion of early atomic models and how scientists represented the rearrangement of atoms in chemical reactions. Students use this historical context to refine their own explanations for how new substances can form while the total amount of matter stays the same.
Finally, students use all of their investigations to build a complete explanation for what happens when substances interact, drawing on evidence about mass, properties, and particle behavior. In the closing lessons, they explore how substances have unique odors based on their molecular structures, linking back to how we detect and identify different materials in everyday life. By the end of the unit, students have developed a complete picture of how matter can change form and structure—producing something new without creating or destroying what was there to begin with.
