States of Matter
KS2SC-KS2-D008
Chemistry domain covering solids, liquids and gases, changes of state when heated or cooled, and the water cycle including evaporation and condensation. Year 4 only.
National Curriculum context
States of Matter at KS2 introduces pupils to the particle model as the scientific explanation for the properties and behaviour of solids, liquids and gases. Pupils compare and group materials together according to whether they are solid, liquid or gas at room temperature, and investigate the processes of evaporation and condensation in the context of the water cycle. The statutory curriculum requires pupils to observe that some materials change state when they are heated or cooled, and to measure or research the temperature at which this happens. This provides the conceptual foundation for understanding thermodynamics, chemical reactions and the physical geography of the water cycle at later stages.
3
Concepts
2
Clusters
2
Prerequisites
3
With difficulty levels
Lesson Clusters
Identify and describe the three states of matter by their properties
introduction CuratedThe three states of matter and their observable properties establish the foundational classification that enables understanding of changes of state and the water cycle.
Explain changes of state and the water cycle using evidence
practice CuratedChanges of state and the water cycle are directly linked in the co_teach_hints (C036 co-teaches with C035); evaporation and condensation are both change-of-state processes and key water cycle mechanisms.
Teaching Suggestions (1)
Study units and activities that deliver concepts in this domain.
States of Matter and the Water Cycle
Science Enquiry Observation Over TimePedagogical rationale
Observation over time is the ideal enquiry type for evaporation because the process is too slow for a single lesson but produces clear, measurable results over a week. Combining hands-on state change demonstrations with the longer evaporation investigation helps pupils connect everyday experiences (puddles drying, windows steaming) to the scientific model of particle behaviour.
Prerequisites
Concepts from other domains that pupils should know before this domain.
Concepts (3)
Three States of Matter
knowledge AI DirectSC-KS2-C034
Understanding that materials can be classified as solids, liquids or gases based on their observable properties. Solids hold their shape; liquids form a pool but not a pile; gases escape from unsealed containers and are not visible.
Teaching guidance
Sort a collection of materials into solids, liquids and gases based on observable properties. Investigate borderline cases — is sand a solid or a liquid? (Solid, because each grain is solid even though sand pours.) Is toothpaste a solid or a liquid? Introduce the particle model informally: in solids, particles are closely packed and vibrate in fixed positions; in liquids, particles are close but can move around each other; in gases, particles are far apart and move freely. Use physical modelling (pupils acting as particles) to represent each state. Explore gases by trapping air in syringes and balloons.
Common misconceptions
Children commonly think that powders (flour, sand, sugar) are liquids because they pour. They are collections of tiny solids. Some pupils think gases have no mass or do not exist because they are invisible — weighing a balloon before and after inflation can address this. Children may struggle with the concept that the same substance (e.g., water) can exist as a solid, liquid or gas depending on temperature.
Difficulty levels
Naming the three states of matter — solid, liquid and gas — and giving a familiar example of each.
Example task
Name the three states of matter. Give one example of each.
Model response: Solid: ice. Liquid: water. Gas: steam.
Describing the observable properties that define each state: solids hold their shape, liquids take the shape of their container but have a fixed volume, gases fill any container and are often invisible.
Example task
How can you tell if something is a solid, liquid or gas? Describe the properties of each.
Model response: Solids: keep their own shape, can be held, do not flow. Liquids: flow and take the shape of their container, have a flat surface, can be poured. Gases: spread out to fill any space, often invisible, can be compressed (squashed into a smaller space).
Classifying a range of materials into solids, liquids and gases, handling tricky cases (sand, jelly, foam), and beginning to explain states using the particle model.
Example task
Is sand a solid or a liquid? It pours like a liquid. Is toothpaste a solid or a liquid? Explain your reasoning.
Model response: Sand is a solid — each grain of sand is a tiny solid that keeps its shape. Sand pours because the grains are small and loose, but the material itself is solid. If you look at one grain under a magnifying glass, it does not flow or take the shape of a container. Toothpaste is trickier — it behaves like a solid when still (it holds its shape on the brush) but flows like a thick liquid when squeezed. It is actually a mixture that has properties of both states. Using the particle model: in solids, particles are tightly packed and vibrate in fixed positions. In liquids, particles are close but can slide past each other. In gases, particles are spread far apart and move freely.
Using the particle model to explain why each state has its characteristic properties and predicting behaviour in new situations.
Example task
Using the particle model, explain why you can walk through air (a gas) but not through a wall (a solid). Why can you push your hand through water (a liquid)?
Model response: In air (gas), particles are spread far apart with large gaps between them. Your body can push through because the particles move aside easily — they have lots of space and energy to move. In a solid wall, particles are tightly packed in a fixed arrangement with strong forces holding them together. You cannot push through because there are no gaps and the particles cannot be displaced. In water (liquid), particles are close together but can slide over each other — your hand pushes particles aside and they flow around it, then close up behind. This is why liquids flow and take the shape of their container — the particles are not fixed in position like solids, but are closer together than in a gas. The particle model explains all three states with one simple idea: how close the particles are and how much they can move.
Delivery rationale
Science knowledge concept — factual content deliverable with visual representations and adaptive quizzing.
Changes of State
knowledge AI DirectSC-KS2-C035
Understanding that materials change state when heated or cooled: melting (solid to liquid), freezing (liquid to solid), evaporation/boiling (liquid to gas), condensation (gas to liquid). Temperature at which state changes occur can be measured in degrees Celsius.
Teaching guidance
Investigate changes of state practically: melt ice and chocolate, freeze water and fruit juice, observe evaporation from wet surfaces, and collect condensation on a cold mirror held above steam. Measure temperatures at which changes occur using thermometers. Create a diagram showing the cycle of changes: solid ⇌ liquid ⇌ gas, with heating arrows in one direction and cooling arrows in the other. Use the terms melting, freezing, evaporating, boiling and condensing precisely. Investigate factors that affect evaporation rate (temperature, surface area, air movement) through fair test investigations.
Common misconceptions
Children often confuse evaporation with boiling — evaporation occurs at any temperature from the surface of a liquid, while boiling occurs throughout the liquid at a specific temperature. Some pupils think that when water evaporates it disappears or ceases to exist, rather than becoming invisible water vapour in the air. Children may believe that melting and dissolving are the same process — melting is a change of state caused by heat, while dissolving is a solid mixing into a liquid.
Difficulty levels
Knowing that ice turns into water when it gets warm and water turns into ice when it gets cold.
Example task
What happens to ice when you leave it in a warm room?
Model response: The ice melts and turns into water because the room is warm.
Naming the changes of state — melting, freezing, evaporating, condensing — and identifying that heating and cooling cause these changes.
Example task
Match each change of state to its correct name: solid to liquid, liquid to solid, liquid to gas, gas to liquid.
Model response: Solid to liquid: melting. Liquid to solid: freezing. Liquid to gas: evaporation (or boiling). Gas to liquid: condensation.
Explaining changes of state using the particle model, identifying the temperature at which state changes occur, and distinguishing evaporation from boiling.
Example task
What is the difference between evaporation and boiling? Both change liquid water into water vapour.
Model response: Evaporation happens at any temperature from the surface of a liquid — particles at the surface gain enough energy to escape into the air. It is a slow process. Boiling happens throughout the liquid at a specific temperature (100°C for water) — bubbles of gas form inside the liquid and rise to the surface. It is a fast process. Both produce water vapour (an invisible gas), but evaporation can happen at room temperature while boiling requires the liquid to reach its boiling point. Using the particle model: during evaporation, only the fastest particles at the surface escape; during boiling, particles throughout the liquid have enough energy to become gas.
Applying understanding of changes of state to explain everyday phenomena and predict the effects of changing conditions.
Example task
On a cold morning, you can see your breath as a cloud when you breathe out, but on a warm day you cannot. Explain why.
Model response: When you breathe out, your breath contains warm water vapour (invisible gas) from your lungs. On a cold morning, this warm water vapour meets the cold air and rapidly cools down. The cooling causes the water vapour to condense — it changes from an invisible gas into tiny liquid water droplets suspended in the air, which we see as a cloud. On a warm day, the outside air is warm enough that the water vapour stays as an invisible gas — it does not cool down enough to condense. This is the same process that forms clouds in the sky — warm air containing water vapour rises, cools at higher altitudes, and the water vapour condenses into tiny droplets. Condensation happens whenever warm, moist air is cooled below a certain temperature (the dew point).
Delivery rationale
Science knowledge concept — factual content deliverable with visual representations and adaptive quizzing.
The Water Cycle
knowledge AI DirectSC-KS2-C036
Understanding that evaporation and condensation are key processes in the water cycle. Water evaporates from oceans, lakes and land when heated; water vapour condenses to form clouds; precipitation returns water to the surface. Rate of evaporation increases with temperature.
Teaching guidance
Create a physical model of the water cycle using a sealed container with warm water, ice placed on top, and a heat source. Observe evaporation, condensation on the cool surface, and 'precipitation' dripping back down. Label each stage of the cycle and connect to the scientific terms learned in states of matter. Discuss where water evaporates from in nature (oceans, lakes, rivers, soil, plants) and what causes condensation (cooling of water vapour as it rises in the atmosphere). Link to geography — rivers, rainfall patterns, clouds. Investigate how temperature affects evaporation rate.
Common misconceptions
Children often think clouds are made of water vapour — clouds are actually made of tiny liquid water droplets or ice crystals; water vapour is invisible. Some pupils believe rain falls from clouds when they 'get too heavy' or 'burst', rather than understanding the role of further condensation and coalescence. Children may think the water cycle is a one-way process (evaporation → rain) rather than a continuous cycle with water endlessly recycling.
Difficulty levels
Knowing that rain falls from clouds, puddles dry up in the sun, and this happens over and over again.
Example task
Where do puddles go when the sun comes out?
Model response: The water in the puddle dries up — it goes into the air.
Describing the water cycle using the terms evaporation, condensation and precipitation in the correct sequence.
Example task
Describe how water moves in a cycle. Use the words evaporation, condensation and precipitation.
Model response: Water from oceans, lakes and rivers is heated by the Sun and evaporates — it changes from liquid water into invisible water vapour that rises into the air. High up, the air is cooler, and the water vapour condenses into tiny water droplets that form clouds. When the droplets join together and get heavy enough, they fall as precipitation — rain, snow, sleet or hail — back down to the ground, rivers and oceans. Then the cycle starts again.
Explaining the water cycle with reference to temperature driving evaporation and cooling driving condensation, and investigating factors that affect evaporation rate.
Example task
We placed saucers of water in four locations: sunny windowsill, shady corner, next to a fan, in a cupboard. After two days, the sunny and fan saucers were empty. Why does temperature and air movement affect evaporation?
Model response: Heat gives water particles more energy, so more particles escape from the surface as water vapour — that is why the sunny saucer evaporated fastest. Moving air (fan) carries water vapour away from the surface, which means more water can evaporate into the space above — the fan saucer evaporated quickly even without extra heat. The shady corner was cooler with still air, so evaporation was slower. The cupboard was enclosed, so the air around the water became saturated with vapour and evaporation slowed. In the water cycle, the Sun provides the heat and wind moves the moist air, driving the global evaporation process.
Explaining the water cycle as a closed system where no water is created or destroyed, and applying this to environmental issues.
Example task
If the same water has been cycling around the Earth for billions of years, why do some places have water shortages?
Model response: The total amount of water on Earth stays the same — it just changes state and location. Water shortages happen because the water cycle does not distribute water evenly. Some regions receive very little precipitation because of their geography and climate patterns. Additionally, much of Earth's water is in the oceans (salty, not drinkable) or locked in ice caps. Only a tiny fraction is accessible fresh water. Human activities also contribute to shortages: over-extraction of groundwater, pollution making water unusable, and climate change altering rainfall patterns. The water cycle ensures water is continuously recycled, but it does not guarantee it arrives where and when humans need it. This is why water conservation and management are so important.
Delivery rationale
Science knowledge concept — factual content deliverable with visual representations and adaptive quizzing.