Same Particles, Different Spacing

◆ Science 7 · Term 1 · Week 4

Name: Section: Date:

Teacher: One page per learner, printed A4. Sections A and B count toward Written Works; see <code>assessment.md</code> §1. Item ★ is the diagnostic — it cannot be answered from the wall chart, because the wall chart's pictures are exactly what it asks the learner to criticise. The key below is screen-only and will not print.

A Draw the particles — same size circles in all three boxes

Solid

Liquid

Draw the gas in the space beside this line: Label each box with the arrangement, the spacing and the motion.

B Which way did the energy go — in or out, and what happens to the spacing

The change	Energy in or out?	Spacing
Ice melting
Water boiling
Steam condensing
Water freezing

C True or false — and correct every false one

Statement	T / F	If false, the correction
Particles get bigger when heated.
There is air in the gaps between particles.
Particles in a solid do not move at all.
Boiling needs more energy than melting.

D The puddle — a puddle on the concrete dries at 30 °C without boiling

What I observed

What the model says is happening

The two boxes are the same size on purpose. A model explains an observation; it does not replace it.

★ The challenge — criticise a drawing

A student draws steam with bigger circles than ice, far apart, with tiny dots labelled air in the gaps. Name two things wrong with it.
Why can there not be air in the gaps?
A model is useful partly because of what it forbids. Name one thing the particle model forbids, and one everyday fact that would be impossible if the model were wrong.

Answer key — screen only, not printed.
A · Solid: regular pattern, touching, vibrating in place. Liquid: close, no pattern, sliding. Gas: far apart, no pattern, fast and straight. The circles must be the same size in all three. A drawing with bigger circles in the gas box scores nothing for spacing, however good the labels. B · in / increases a little · in / increases enormously · out / decreases · out / decreases. C · F — the spacing increases, not the particles · F — there is nothing there · F — they vibrate in place · T. D · varies. The right-hand box should say that the fastest particles at the surface escape. ★ This is the diagnostic. Item 1: the circles should be the same size, and there should be nothing in the gaps. Item 2: air is itself made of particles, which would need gaps between them, and so on without end. Item 3 is the one that reads — a learner who can name something the model forbids has understood that a model is a set of claims rather than a picture. Accept: particles cannot swell, cannot melt individually, cannot be created by heating. For the everyday fact, accept compressing a gas, a sealed can bursting, sweat cooling, or a puddle drying below boiling.