---
marp: true
theme: default
html: true
---

# Why can you squash air but not water?

Year 7 Chemistry · Particle theory

<!-- Speaker note: Students use particle theory to explain physical properties (compressibility, density, viscosity), naming the arrangement, motion or attraction behind each (AC9S7U05, node 3, a hinge node for all of AC9S7U06). About 25 minutes (Engage and Explore 10 min · Explain 8 min · Evaluate 3 min · Typical adds 5 min, Wider about 15 min). -->

---

## Today

**We are learning to** use particle theory to explain physical properties (how easily a substance squashes, its density, how it flows) by naming the arrangement, motion or attraction behind each one.

- I can explain why gases can be squashed and liquids and solids can't.
- I can explain why a gas is less dense than a liquid using particle spacing.
- I can name the particle feature (arrangement, motion or attraction) behind a property.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea. Set the width with `?width=minimum`, `typical` (default) or `wider`. This is the hinge into pure substances and mixtures: every separation technique in AC9S7U06 is chosen by explaining property differences at the particle level. Students who can only label diagrams stall there. Teacher: Follow up with real sealed syringes of air and water if you have them. -->

---

## Why it matters

> Seal the end of a syringe full of air and you can push the plunger a long way in. Do the same with water and it barely moves. Particle theory explains why, and the same explanation works for density, runny honey and smells crossing a room.

<!-- Speaker note: This lesson moves from describing particles to **explaining properties** with them. Every explanation names a particle feature: arrangement, motion or attraction. -->

---

<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

**Three sealed syringes hold a solid plug of wax, water, and air. You push each plunger as hard as you can. Which plunger moves in the furthest?**

- Wax
- Water
- They all move the same amount
- Air

<!-- Speaker note: What happens: Only the air squashes. Its particles are far apart, with empty space to move into. Wax and water particles are already close together. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: ask a student who chose water or wax to say why. Listen for 'the particles squash'. -->

---

<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%2Fproperties%2Fstep-2&code=widget%3A+syringe%0A}}

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

<!-- Speaker note: For each substance: push the plunger all the way in, then pull it back out and record how many particles sit in the dashed window. The window is the same size for every substance. -->

<!-- Speaker note: Teacher: the window count is the density idea. Point out that air's count is so low it is often 0 or 1. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<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?

* Only the air squashes. Its particles are far apart, with empty space to move into. Wax and water particles are already close together.

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

---

<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 water syringe

**Why does the plunger stop in the water syringe?**

- The water particles are too hard to squash
- The water particles are already close together, so there is almost no space to push them into
- The water particles stop moving when pushed
- Water is heavier than air

* Answer: The water particles are already close together, so there is almost no space to push them into

<!-- Speaker note: The particles stay the same size; there is just no empty space left. -->

<!-- Speaker note: Teacher: insist on a particle feature in every sentence of the written explanation. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 27px; }</style>

---

<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>

## Density

**Why is air much less dense than water?**

- Air particles are smaller
- Air particles are far apart, so there are far fewer in each cm³
- Each air particle is lighter than a water particle
- Air has no mass

* Answer: Air particles are far apart, so there are far fewer in each cm³

<!-- Speaker note: Fewer particles in each cm³ means less mass in each cm³: lower density. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 27px; }</style>

---

<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>

## Mix it up

**Looking back at the particle model: a drop of water is heated until it becomes steam. What happens to the water particles?**

- They disappear
- They get bigger
- They break into smaller pieces
- They stay the same size, but move faster and spread far apart

* Answer: They stay the same size, but move faster and spread far apart

<!-- Speaker note: Ice, water and steam are the same particles. Only their arrangement and motion change, so any squashing comes from the space between them. What this step is for: Particles never change size: the same particles in a different arrangement explain the three states, and this lesson depends on it. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<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>

## Elaborate: three substances

**Honey, water and air. Which particle feature best explains each observation?**

Groups: Arrangement: how close and ordered the particles are · Motion: how fast the particles move · Attraction: how strongly particles pull on each other

Honey pours much more slowly than water. · Air can be squashed but water can't. · Water is about 800 times denser than air. · The smell of honey spreads through a whole room. · Warm honey pours faster than cold honey.

* Answer: Honey pours much more slowly than water. → Attraction: how strongly particles pull on each other; Air can be squashed but water can't. → Arrangement: how close and ordered the particles are; Water is about 800 times denser than air. → Arrangement: how close and ordered the particles are; The smell of honey spreads through a whole room. → Motion: how fast the particles move; Warm honey pours faster than cold honey. → Motion: how fast the particles move

<!-- Speaker note: Honey and water have the same arrangement but behave differently: attraction makes the difference. What this step is for: Honey and water share an arrangement but not an attraction: comparing three substances makes students choose the feature. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 16px; }</style>

---

<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: float or sink

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry%2Fproperties%2Fstep-6&code=widget%3A+windows%0Aset%3A+floatsink%0Acaption%3A+Each+window+is+1+cm%C2%B3.%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry/properties/?full=step-6#step-6)

<!-- Speaker note: Each window is 1 cm³. Iron particles are packed tightly and each one is heavier. Foam is mostly trapped air, so a window of foam holds very few particles. What this step is for: Packing per cm³ links node 3's density to floating, a new context for the same idea. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<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>

## Foam

**Will a block of foam float on water?**

- Floats
- Sinks

* Answer: Floats

<!-- Speaker note: Foam is mostly trapped air: less mass in each cm³ than water, so it floats. -->

---

<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>

## Iron

**Will a block of iron float on water?**

- Floats
- Sinks

* Answer: Sinks

<!-- Speaker note: Iron packs far more mass into each cm³ than water, so it sinks. -->

---

<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: diffusion

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry%2Fproperties%2Fstep-7&code=widget%3A+diffusion%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry/properties/?full=step-7#step-7)

<!-- Speaker note: Two colours of the same substance start on opposite sides of a barrier. When it lifts, they mix: this is **diffusion**. Predict first: will the gas or the liquid mix faster? Then time both. What this step is for: Diffusion is motion plus space: the same model predicts which state mixes faster. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<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?

**Why did the gas mix faster?**

- Gas particles are smaller
- Gas particles move fast and have lots of space to move into
- The liquid particles stop moving

* Answer: Gas particles move fast and have lots of space to move into

<!-- Speaker note: In the liquid, particles keep bumping into close neighbours, so they spread slowly. -->

---

<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: mystery substance X

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry%2Fproperties%2Fstep-8&code=widget%3A+box%0An%3A+44%0Ajit%3A+0.12%0Acolour%3A+p3%0Acaption%3A+Substance+X%3A+particles+close+together%2C+no+pattern%2C+sliding+slowly+past+each+other+because+they+attract+strongly.%0A}}

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

<!-- Speaker note: What this step is for: Predicting properties from a diagram, then checking real data, is the strongest test that students can use the model. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<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>

## Squashing

**Can X be squashed easily?**

- Yes, easily
- No, hardly at all

* Answer: No, hardly at all

<!-- Speaker note: Its particles are already close together. -->

---

<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>

## Flowing

**Does X flow?**

- No, it holds its shape
- Yes, easily like water
- Yes, but slowly

* Answer: Yes, but slowly

<!-- Speaker note: No fixed pattern, so it flows; strong attraction makes it slow. -->

---

<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>

## Warming

**If you warm X, how does its flow change?**

- It flows slower
- It flows faster
- No change

* Answer: It flows faster

<!-- Speaker note: X is glycerol, a syrupy liquid used in soap and cough syrup. It barely compresses, pours roughly a thousand times more slowly than water at room temperature, and runs much more freely when warm. -->

---

## Evaluate: look back

Which syringe did you predict would move furthest, and why? Write one sentence: "At first I thought… Now I think… because…"

**Revision summary**

- Gases can be squashed because their particles are far apart, with lots of empty space between them.
- Solids and liquids hardly squash at all: their particles are already close together.
- Gases are much less dense because there are far fewer particles in each cm³. The same substance as a solid or a liquid has a similar density: its particles are close together in both.
- The particles themselves never shrink or squash. Only the spaces between them change.

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 23px; }</style>

---

<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

**Why is steam much less dense than the same mass of liquid water?**

* It is the same particles, but in steam they are far apart, so the same mass takes up much more space.

<!-- 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: AC9S7U06 node 1, pure substances and mixtures at the particle level. In class: sealed syringes of air and water; a density column of honey, water and oil. -->