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# Same particles, new look?

Year 8 Chemistry · Chemical change

<!-- Speaker note: Students explain physical change as the same particles rearranged, spread out or packed together, with no new substance formed, and represent it with the particle model (AC9S8U07, node 1). About 24 minutes (Engage and Explore 8 min · Explain 10 min · Evaluate 3 min · Typical adds 3 min, Wider about 3 min). -->

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## Today

**We are learning to** in a physical change (melting, boiling, dissolving) the particles move, spread out or pack together, but every particle stays the same: no new substance is made. Steam is still made of water particles.

- I can explain a physical change at the particle level.
- I can say what changes and what stays the same in a physical change.
- I can draw particle diagrams of a physical change.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea. Set the width with `?width=minimum`, `typical` (default) or `wider`. It comes after Elements and compounds and before Is it a new substance? (chemical change, node 2), which uses the same boards to compare. Not a hinge node, but its misconceptions return in chemical change: boiling splits water into hydrogen and oxygen; particles expand when heated; dissolved substances are destroyed. The prediction tests the first. Board notes: the heat board shows water's particles as single dots (not their atoms); the steam board shows each particle's atoms. Real steam is invisible; the white cloud above a kettle is tiny drops of liquid water. The dissolve board's salt particles stand for sodium and chloride ions. Teacher: In your own words: the three boxes drawn with the same symbol for water are the evidence. -->

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## Why it matters

> A puddle disappears on a hot day. A sugar cube vanishes in tea. Has anything actually gone?

<!-- Speaker note: You know particles are atoms, alone or joined. This lesson asks what happens to them when something melts, boils or dissolves. -->

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<span style="background:#dbeafe; color:#1a1a1a; border:1.5px solid #3b82f6; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">💬 Discussion</span>

## Engage: predict

**Water boils in a kettle and bubbles rise. What are the bubbles made of?**

- Water particles that have grown bigger
- Air that was hiding in the water
- Hydrogen and oxygen, split off from the water
- Water particles (steam), far apart

<!-- Speaker note: What happens: Water particles, as steam. Boiling only gives the particles enough energy to escape each other and spread out; each one is still H₂O. Nothing new is made, so boiling is a physical change. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: tally the predictions. 'Hydrogen and oxygen' is the one to come back to in the Typical step. -->

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<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Fphysical-change%2Fstep-2&code=widget%3A+heat%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/physical-change/?full=step-2#step-2)

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: ask whether any new kind of particle appeared, and what did change. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What happened?

* Water particles, as steam. Boiling only gives the particles enough energy to escape each other and spread out; each one is still H₂O. Nothing new is made, so boiling is a physical change.

<!-- Speaker note: Reveal after running. Ask who predicted it, and what made them think so. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## The particles

**In melting, boiling and dissolving, what happens to the particles?**

- They change how they are arranged and how they move, but stay the same particles
- They turn into new particles
- They get bigger as they warm up

* Answer: They change how they are arranged and how they move, but stay the same particles

<!-- Speaker note: A physical change rearranges the same particles. Nothing new is made. -->

<!-- Speaker note: Teacher: the 'what changes' sort and the physical-or-not sort are the success criteria. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What changes

**Physical change: what changes, and what stays the same?**

Groups: Changes · Stays the same

How the particles are arranged · How fast the particles move · The spaces between the particles · The atoms inside each particle · The number of particles · The substance

* Answer: How the particles are arranged → Changes; How fast the particles move → Changes; The spaces between the particles → Changes; The atoms inside each particle → Stays the same; The number of particles → Stays the same; The substance → Stays the same

<!-- Speaker note:  -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Physical or not

**Physical change or not?**

Groups: Physical change · Not physical: a new substance forms

Butter melting · Water vapour forming drops on a cold window · Sugar dissolving in tea · Cutting paper into pieces · Toast burning · An iron nail rusting

* Answer: Butter melting → Physical change; Water vapour forming drops on a cold window → Physical change; Sugar dissolving in tea → Physical change; Cutting paper into pieces → Physical change; Toast burning → Not physical: a new substance forms; An iron nail rusting → Not physical: a new substance forms

<!-- Speaker note:  -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Where the salt went

**Salt dissolved in water seems to disappear. How could you show it is still there?**

- Filter it out with filter paper
- You can't: dissolved salt is destroyed
- Evaporate the water: the salt is left behind

* Answer: Evaporate the water: the salt is left behind

<!-- Speaker note: The salt particles are spread between the water particles. Evaporating the water leaves them behind as crystals. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Why it can be reversed

**Melting, boiling and dissolving can usually be reversed. Why?**

- Being reversible is what makes a change physical
- Any change can be reversed if you try hard enough
- No energy goes in or out, so nothing is lost
- The same particles are still there, so they can be brought back to how they were

* Answer: The same particles are still there, so they can be brought back to how they were

<!-- Speaker note: No new substance is made, so the original particles are all still there to rearrange back. Being reversible is a result of a physical change, not what defines it. -->

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<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: inside the steam

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Fphysical-change%2Fstep-4&code=widget%3A+atoms%0Ashow%3A+H2O+x12%0Atemp%3A+420%0Acaption%3A+Steam%2C+enlarged+millions+of+times.%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/physical-change/?full=step-4#step-4)

<!-- Speaker note: What this step is for: Inspecting the atoms of steam particles answers the bubbles question directly: still H₂O, not hydrogen and oxygen. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What's inside

**What is in each steam particle?**

- Air
- Separate hydrogen and oxygen atoms
- Two hydrogen atoms joined to one oxygen atom: H₂O, the same as liquid water

* Answer: Two hydrogen atoms joined to one oxygen atom: H₂O, the same as liquid water

<!-- Speaker note: Steam is water as a gas: the same H₂O particles, moving fast and far apart. -->

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<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: does mass change?

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-8%2Fphysical-change%2Fstep-5&code=widget%3A+heat%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-8/physical-change/?full=step-5#step-5)

<!-- Speaker note: What this step is for: Keeping track of the particles explains why mass stays the same in a physical change, even when volume changes. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## The mass

**100 g of ice melts in a sealed bag. What is the mass of the water?**

- 100 g: the same particles, so the same mass
- Less than 100 g: water takes up less space
- More than 100 g: liquids are heavier

* Answer: 100 g: the same particles, so the same mass

<!-- Speaker note: No particles are made or lost in a physical change, so the mass stays the same. (Ice is actually a little less dense than water, which is why it floats.) -->

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## Evaluate: look back

Write one sentence: "At first I thought… Now I think… because…"

**Revision summary**

- In a **physical change** (melting, freezing, boiling, condensing, dissolving, cutting) the particles change how they are arranged, how far apart they are and how fast they move.
- The particles themselves stay the same, so **no new substance** is made. Steam is still water; dissolved salt is still salt.
- The number of particles stays the same, so the **mass** stays the same.
- Next lesson: a **chemical change**, where atoms rearrange into new particles.

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Exit ticket

**Wax melts on a candle and drips. Use particles to explain why this is a physical change.**

* The wax particles move from fixed positions to sliding past each other, but each particle is still wax: no new substance, so physical.

<!-- Speaker note: Students answer on paper or a mini whiteboard before the reveal. Anyone who cannot answer needs the main idea again next lesson. Where this leads: Next: Is it a new substance? (chemical change, node 2), which uses the melting and dissolving boards again to compare with a reaction. In class: melting chocolate or wax, condensation on a cold can, dissolving and recovering salt by evaporation; weigh ice in a sealed bag before and after melting. -->