--- title: "What can't the particle model explain?" subtitle: "Year 7 Chemistry · Particle theory · Lesson 5" --- # What can't the particle model explain? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** A street map is perfect for finding a café and useless for knowing how steep the hill is. Scientific models are like that too. :::teacher-note **In one sentence:** Students identify what the particle model explains well and what it can't, reason from its assumptions to its limits, and name evidence for it (AC9S7U05, node 5). **Students should be able to say:** I can name something the particle model explains well, and why. I can name something it can't explain, and why. I can give evidence for the particle model. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **The particle model can't explain why copper is orange. What does that mean?** ☐ Colour is not real ☐ Copper isn't made of particles ☐ The model is wrong and should be thrown away ☐ The model has limits: it is still useful for what it does explain My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** The model has limits. It treats particles as plain balls with no parts, so it can't explain colour. It still explains states, diffusion and pressure very well, so scientists keep using it, alongside other models for other jobs. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: scope and limits :::keep-together ### Can it explain it? **Can the particle model explain it?** Groups: Explains it well, Can't explain it - A smell spreading across a room: {{field-15}} - Air being easy to squash but water not: {{field-15}} - A metal bar getting longer when heated: {{field-15}} - Why copper is orange and gold is yellow: {{field-15}} - Why iron rusts but gold doesn't: {{field-15}} - Why metals conduct electricity: {{field-15}} ::: :::teacher-note **Answer:** A smell spreading across a room → Explains it well; Air being easy to squash but water not → Explains it well; A metal bar getting longer when heated → Explains it well; Why copper is orange and gold is yellow → Can't explain it; Why iron rusts but gold doesn't → Can't explain it; Why metals conduct electricity → Can't explain it ::: :::keep-together ### Reactions **Why can't the particle model explain why some substances react?** ☐ Because the model only works for gases ☐ It treats particles as plain balls with no parts, so it says nothing about how they could join or swap ☐ Because reactions are too fast to see ::: :::teacher-note **Answer:** It treats particles as plain balls with no parts, so it says nothing about how they could join or swap To explain a phenomenon, a model needs the right parts. Reactions need atoms that can join and rearrange (Year 8), and electricity needs electrons (Year 9). ::: :::keep-together ### Evidence **What evidence supports the particle model?** ☐ We can see particles with our eyes ☐ Diffusion, gases being compressible, and tiny specks in water jiggling under a microscope ☐ It explains everything ::: :::teacher-note **Answer:** Diffusion, gases being compressible, and tiny specks in water jiggling under a microscope The jiggling of tiny grains from pollen in water (Brownian motion) is the particles of water knocking them about: strong evidence, explained by Einstein in 1905. ::: :::keep-together ### Why it explains smells **The particle model explains a smell spreading across a room. Which part of the model does the explaining?** ☐ The smell spreads only because a breeze carries it ☐ Smell particles get bigger until they fill the room ☐ Particles are always moving, with space between them, so the smell's particles spread out between the air particles ☐ Smell particles are lighter than air, so they float up and spread ::: :::teacher-note **Answer:** Particles are always moving, with space between them, so the smell's particles spread out between the air particles What the model assumes (moving particles with space between them) is exactly what diffusion needs. That is why it explains it well. ::: ## Mix it up :::keep-together **Looking back at squashing: a syringe of air can be squashed, but a syringe of water cannot. What does the particle model say is different?** ☐ Air has no mass, so nothing pushes back ☐ Air particles are smaller than water particles ☐ Air particles are far apart, with space to move into; water particles are already close together ☐ Water particles are harder than air particles ::: :::teacher-note **Answer:** Air particles are far apart, with space to move into; water particles are already close together The spacing explains it. This is the kind of job the particle model does well: explaining how substances behave from the arrangement and motion of their particles. ::: :::typical ## Elaborate: a better model :::keep-together **In Year 8 the particles get parts: they are made of atoms of different types that can join. What can this new model explain that the plain particle model couldn't?** ☐ Why substances react and make new substances ☐ Why smells spread ☐ Why gases are easy to squash ::: :::teacher-note **Answer:** Why substances react and make new substances A new model keeps what the old one did well and adds what it couldn't do. Scientists choose the simplest model that does the job. ::: ::: :::wider ## Elaborate: how the idea grew :::keep-together **Ancient Greek thinkers suggested matter is made of tiny particles, but most people didn't accept it for over 2000 years. What changed?** ☐ It was voted on ☐ Someone saw a particle ☐ Evidence: experiments on gases, chemical reactions and Brownian motion that the idea explained and predicted ::: :::teacher-note **Answer:** Evidence: experiments on gases, chemical reactions and Brownian motion that the idea explained and predicted Models are accepted when they explain and predict evidence better than the alternatives, and changed when new evidence doesn't fit. ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - The particle model says matter is made of tiny particles that move and attract each other. - It explains states, diffusion, compressing gases and expansion very well, and evidence such as diffusion and Brownian motion supports it. - It can't explain colour, reactions or electricity, because its particles are plain balls with no parts. - Every model has a scope and limits. Scientists keep a model for what it does well and use or build other models for the rest. ## Exit ticket :::keep-together **Name one thing the particle model explains well and one thing it can't, with a reason for each.** {{lines-3}} ::: :::teacher-note **Answer:** For example: explains diffusion (particles move and mix); can't explain colour (particles are plain balls with no parts). :::