Year 8 Science · Unit 3 · Lesson 13
Apply Worksheet
Learning Goals
Compare two
Complete the table to compare particle models and word equations as ways of representing chemical change.
| Feature | Particle Model (ball-and-stick) | Word Equation |
|---|---|---|
| What it shows about atoms/molecules | ||
| What it shows about bond breaking and forming | ||
| How easy it is for a beginner to understand | ||
| One important limitation | ||
| More useful for (which audience and why) |
Scenario
A student draws a particle model of a chemical reaction. On the left side (reactants) they show 3 oxygen atoms bonded as O₂ and O. On the right side (products) they show only 2 oxygen atoms in a water molecule. The student claims this is a valid model of the reaction because "atoms can be used up during chemical reactions."
(a) Predict whether this model is scientifically valid. State your prediction clearly.
(b) Use the law of conservation of mass to explain why the student's model is incorrect. What must always be true of the atoms on both sides of a valid particle model?
(c) Give one example of a limitation of ball-and-stick particle models that is NOT related to conservation of mass. Explain why this limitation exists.
Wrap Up
In one sentence, what was the main idea of this lesson?