S1 Science | States of matter and the particle model: a tutor prep guide (three-column frame, heating curve plateaus)

2026-11-12

Tutor lesson-prep guides · Secondary science

Students say particles are packed in solids, closer in liquids and far apart in gases, then go blank when asked why a gas compresses and water does not. The gap is not memory, it is a missing answer frame. This lesson teaches one three-column table: arrangement, spacing, motion. Every question is answered from those three columns, including the two plateaus on a heating curve.

Objectives — Students can: (1) describe solids, liquids and gases using the same three columns, arrangement, spacing and motion; (2) use the particle model to explain three observations: a gas compresses while a liquid barely does, gases diffuse easily, and a solid keeps its shape while a liquid does not; (3) name the six changes of state (melting, freezing, boiling, condensing, sublimation, deposition) and state which two skip the liquid state; (4) read the two plateaus of a heating curve and explain that temperature stays constant while energy is still absorbed, at 0 degrees C and 100 degrees C for water at 1 atm.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Names of the states	What state are ice, water and steam?	Solid, liquid and gas
Heat and temperature	Does heating always raise the temperature?	No. During a change of state the temperature can stay constant
Particle idea	If water is made of tiny particles, is there space between them?	Yes. The gaps are largest in a gas

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-5 min	Estimate first	Show three containers (ice, water, air) and ask which can be compressed	Vote and give one reason
5-15 min	Three columns	Draw arrangement, spacing, motion on the board and fill all three states	Place each state in the frame
15-25 min	Three observations	Derive compressibility, diffusion and fixed shape from the frame; drop ink into water	Explain one observation using two columns
25-35 min	Six changes	Draw the arrow chart with direction and heat absorbed or released; mark sublimation and deposition	Place the six names on the arrows
35-41 min	Heating curve	Draw the ice curve; mark both plateaus at 0 and 100 degrees C, and that heating continues	Point to the flat sections
41-45 min	Exit check	Collect three items, mark on the spot, name the scene to reteach	Hand in three items

03 Teaching script (read it out)

Scene 1: Scene 1: One frame, four questions

“From today every question about states is answered in the same three columns: arrangement (ordered or random), spacing (close or far), motion (vibrating in place or moving freely). Solid: ordered, closest, vibrating in fixed positions. Liquid: random, close, able to slide. Gas: fully random, furthest apart, fast and free. Write all three columns and you score even if your sentences are plain.”

All three states answered in the order arrangement, spacing, motion.

Scene 2: Scene 2: Three observations from the same frame

“Compressibility is about spacing: gas particles are furthest apart with the most empty space, so a syringe pushes in; liquid particles are already close, so it barely moves. Diffusion is about motion: gas particles move fast and freely, so a perfume smells across the room; liquid particles only slide, so sugar needs stirring. Fixed shape is about arrangement: solid particles are locked in place, liquid particles slide past each other and take the container shape. Three observations, one frame, nothing extra to memorise.”

Spacing explains compression, motion explains diffusion, arrangement explains shape.

Scene 3: Scene 3: The two plateaus on a heating curve

“Ice warms from below zero to 0 degrees C and then stops. It is still being heated, but the temperature does not rise, because the energy is breaking the ordered arrangement instead of speeding the particles up. That flat section is the melting point. Once everything has melted the temperature rises again, then stops at 100 degrees C: the second plateau is the boiling point. So an answer needs two sentences: temperature constant, yet energy still absorbed, and the energy changes the arrangement of particles.”

A plateau means constant temperature with heat still absorbed, used to change arrangement.

04 Question types and worked steps

Type	Example	Steps	Answer
Three-column explanation	Why does a gas compress while water barely does?	(1) Compare spacing (2) gas particles are furthest apart with lots of empty space (3) liquid particles are close with little empty space (4) so the gas compresses and the liquid hardly does	Gas particles are widely spaced; liquid particles are close together
Naming a change	Mothballs in a wardrobe shrink and smell. Which change of state is it?	(1) Solid turning directly into gas (2) no liquid stage (3) solid to gas is sublimation (4) the reverse, gas to solid, is deposition	Sublimation, solid straight to gas
Heating curve	A heating curve for ice is flat at 0 degrees C. Is heat still being absorbed there?	(1) Heating continues (2) temperature stays constant (3) energy breaks the ordered arrangement as solid becomes liquid (4) so heat is absorbed without a temperature rise	Yes, heat is absorbed and used for melting
Density comparison	Ice is 0.92 g/cm3 and water is 1.00 g/cm3. Why does ice float?	(1) Lower density (2) less mass in the same volume (3) the difference is 0.08 g/cm3, about 8 percent (4) so ice floats on water	Ice at 0.92 is below water at 1.00, about 8 percent less

Sanity check (teach this): Sanity checks: (1) use 0 degrees C and 100 degrees C only for water at 1 atm, never transfer them to other substances; (2) a plateau needs both statements, constant temperature and heat still absorbed, or the explanation mark is lost; (3) ice is 0.92 g/cm3 and water 1.00 g/cm3, a difference of 0.08, so never say the densities are nearly the same; (4) 1 cm3 of water becomes about 1600 cm3 of steam, which is evidence of wider spacing, not of more substance; (5) sublimation and deposition skip the liquid state while the other four pass through it; (6) the particles themselves do not change size, only arrangement, spacing and motion do.

05 Independent practice (3 questions)

Question	Answer	What to watch
Describe a liquid and a gas using the three columns.	Liquid: random arrangement, close spacing, particles slide. Gas: fully random, furthest apart, fast free motion.	All three columns for full marks
Name the six changes of state and the two that skip the liquid state.	Melting, freezing, boiling, condensing, sublimation, deposition; sublimation and deposition skip the liquid state	Six names plus two exceptions
Explain why the temperature is constant on a plateau.	The energy changes the arrangement of particles rather than their motion, so heat is absorbed without a temperature rise	The purpose of the energy must be named

06 Common mistakes and what to say

Mistake	Student writes	Say this
Particles growing	Heating makes the particles bigger, so the substance expands	“The particles do not grow; the spacing and the motion change. Writing that particles grow is a conceptual error.”
Plateau as no heating	The flat part at 0 degrees C means the heating was switched off	“The flame keeps burning; the energy goes into melting, which is why the temperature stays flat.”
Sublimation as evaporation	Mothballs evaporate	“Evaporation is liquid to gas. Mothballs go solid to gas, which is sublimation.”
Densities nearly equal	Ice and water have almost the same density, so ice floats	“0.92 against 1.00 is 8 percent different; saying nearly the same leaves you unable to explain floating.”

07 Homework (paper, section and question numbers)

Secondary prep guide overview — Other chapters in this subject; the particle model underpins later chemistry
Previous chapter: lab safety and apparatus — Heating and measuring are the practical skills needed before the heating-curve experiment
Extension: primary general studies on states and dissolving — The same topic at primary level, useful to tell whether a student lacks the phenomenon or the explanation

08 Exit check (last 5 minutes)

Question	Answer	Decision
What are the three columns?	Arrangement, spacing, motion	Reteach scene 1
Is heat absorbed during a plateau?	Yes, temperature is constant but heat is still absorbed to change the arrangement	Reteach scene 3
Which two changes skip the liquid state?	Sublimation (solid to gas) and deposition (gas to solid)	Reteach the 25-35 min block

09 Tutor FAQ

Why not just teach that solid particles are packed in a regular pattern?

Because students repeat one sentence and cannot answer explanation questions. The three columns force three elements every time, so compression, diffusion and shape questions all use the same frame.

Must we draw the heating curve?

Yes. The plateau is visual memory and one drawing beats ten explanations. Label 0 and 100 degrees C and write that heat is still absorbed next to each plateau.

Should we link diffusion to temperature?

One line is enough: higher temperature means faster particle motion and faster diffusion. S1 does not need calculations, only the causal link.

Find a tutor — free Tutor Registration →

A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.