Year 4: States of matter
States of matter
Curriculum Requirement
- compare and group materials together, according to whether they are solids, liquids or gases
- observe that some materials change state when they are heated or cooled, and measure or research the temperature at which this happens in degrees Celsius (°C)
- identify the part played by evaporation and condensation in the water cycle and associate the rate of evaporation with temperature
Pupils should explore a variety of everyday materials and develop simple descriptions of the states of matter (solids hold their shape; liquids form a pool not a pile; gases escape from an unsealed container). Pupils should observe water as a solid, a liquid and a gas and should note the changes to water when it is heated or cooled.
Note: Teachers should avoid using materials where heating is associated with chemical change, for example, through baking or burning.
Pupils might work scientifically by: grouping and classifying a variety of different materials; exploring the effect of temperature on substances such as chocolate, butter, cream (for example, to make food such as chocolate crispy cakes and ice-cream for a party). They could research the temperature at which materials change state, for example, when iron melts or when oxygen condenses into a liquid. They might observe and record evaporation over a period of time, for example, a puddle in the playground or washing on a line, and investigate the effect of temperature on washing drying or snowmen melting.
National Curriculum in England: primary curriculum, Section: "States of matter", p. 162-163.
What is Everything Made Of?
Everything you can touch, see, or even breathe is made of 'matter'. Matter is the 'stuff' that makes up our world, from the biggest mountain to the smallest ant. The air we breathe, the food we eat, and the water we drink is all made of matter.
This stuff comes in three main states: Solid, Liquid, and Gas.
The Three States of Matter
Solids
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Solids are things you can hold. They keep their own shape.
A rock is a solid, and so is an ice cube, your desk, or a book.
How to identify:
It has a fixed shape that doesn't change, even if you move it.
💡 Fun Facts
- Solids always take up the same amount of space (they have a fixed volume).
- The tiny particles (called atoms) inside a solid are packed very tightly together and just vibrate on the spot.
- Even something soft like a sponge or a teddy bear is a solid—it doesn't flow like water. A cushion or soft toy can change shape and size because its made of a solid that is woven and is mostly full of air.
- Water is actually a very pale blue. It's so pale you can't tell by looking through a glass of water, but when you see a frozen glacier that is made of thick frozen water, the blue colour is quite striking.
Liquids
Liquids flow and take the shape of whatever container they are in.
Water in a glass, rain in a puddle, milk, and honey are all liquids. Streams and rivers are created when water flows to the lowest part of the land and keeps going until it finds a lake to fill up or reaches the sea.
How to identify:Unidentified
It doesn't have its own shape. It flows and takes the shape of the bottom of its container.
💡 Fun Facts
- Liquids are "runny," but some liquids are runnier than others. Water is very runny, but treacle flows very slowly.
- The particles in a liquid are close together but can wiggle and slide past each other, which is why liquids can flow.
- No matter what shape container you pour it into, a liquid always takes up the same amount of space (volume).
Gases
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Gases spread out to fill the entire space they are in. If they are under water then they rise to the surface as bubbles because the water is much heavier.
The oxygen in the air you breathe is a gas. Some gasses are flammable and create heat when they burn. You can't usually see gases, but they are all around you.
How to identify:
It has no fixed shape or volume. It spreads out to fill any container it is in.
💡 Fun Facts
- A gas will expand forever if it's not in a sealed container, just like the air in a balloon.
- The particles in a gas are far apart and zoom around really fast in all directions.
- You can feel a gas when the wind (which is moving air) blows against your face or when you feel the fizz from a fizzy drink.
- If you blow through a straw into a glass of water, the bubbles you see are made from the gasses you are exhaling.
Changing States and The Water Cycle
Matter can change from one state to another when you add heat (energy) or take heat away (cool it down). These changes are happening all around us, all the time.
Heating and Cooling
The Exploding Beetle!
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The Bombardier Beetle has a super-powered defence. When a predator (like an ant or a frog) attacks, it shoots boiling hot spray from its bottom!
How it works:
It stores two special liquids in its body. When it gets scared, it mixes them together. The mix gets hotter than boiling water (100°C) almost instantly! This heat forces the liquid to evaporate into a hot, steamy gas. This gas explodes out with a 'POP!' and scares the attacker away.
💡 Fun Facts
- The spray is not just hot; it's also very stinky!
- The beetle can aim its spray in almost any direction.
- This rapid change from liquid to gas is called 'flash evaporation'.
Melting and Freezing
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When you heat a solid, it can melt into a liquid. When you cool a liquid, it can freeze into a solid.
Melting: Ice (solid) turns into water (liquid). Freezing: Water (liquid) turns into ice (solid).
The temperature where this happens for water is 0°C.
This process of changing state is all about energy. Adding heat energy makes the tiny particles in a solid wiggle faster until they break free, but taking energy away (cooling) makes them slow down and lock back into place.
Different solids have different melting points. An ice cube melts at 0°C, but a solid chocolate bar melts at a warmer temperature (which is why it melts in your hand!), and solid rock needs the incredible heat of a volcano to melt into lava.
💡 Fun Facts
- Chocolate and butter are solids that melt easily when heated, which is why they are great for baking.
- In winter, water in ponds and puddles can freeze to form a solid layer of ice on top.
- Volcanoes shoot out hot, liquid rock called lava, which cools down (freezes) to become solid rock.
- We call 0°C the freezing point of water, but it's also its melting point!
- Water is special: when it freezes into ice, it actually expands (gets bigger). This is why a full, sealed plastic bottle can crack or split open if you leave it in the freezer.
- Snow and hail are solid forms of water. If they fall through air that is warmer than 0°C, they melt on the way down and land as rain. ❄️➡️🌧️
- Even solid metals can melt. Blacksmiths heat iron until it becomes a glowing liquid, then pour it into a mould (a shape) and let it freeze back into a solid, like a horseshoe or a sword.
- Glass is made by melting sand (a solid) at a very high temperature (about 1700°C) into a thick, syrupy liquid, which is then shaped and cooled.
The Frozen Frog
Some frogs, like the Wood Frog in North America, can survive being frozen solid in winter!
How it works:
When winter comes, the frog's body starts to freeze. Its heart stops beating, and it stops breathing. The water (liquid) in its body turns into ice (solid). It becomes a "frog-sicle"! It has special sugar in its blood that protects its important bits from being damaged by the ice. When spring arrives, the frog thaws out (the ice melts back into liquid), its heart starts again, and it hops away!
💡 Fun Facts
- The frog's body can be more than 60% frozen solid.
- This special trick is called cryoprotection ('cold protection').
- This allows the frog to be the first one active in spring, as it doesn't have to burrow deep underground to escape the frost.
Evaporation and Condensation
When you heat a liquid, it can evaporate into a gas. When you cool a gas, it can condense back into a liquid.
Evaporation: Water (liquid) turns into water vapour (a gas) when it warms up. Condensation: Water vapour (gas) turns back into water (liquid) when it cools down.
💡 Fun Facts
- Evaporation is why puddles disappear on a sunny or windy day. The water turns into an invisible gas and mixes with the air.
- Condensation is what makes clouds! The invisible water vapour high in the sky cools down and turns into tiny, visible water droplets.
- You see condensation on a cold day when you breathe out—your warm, damp breath (gas) hits the cold air and turns into a little cloud (liquid).
How Plants "Sweat"
Just like you sweat on a hot day to cool down, plants "sweat" too! This is called transpiration, and it's a key part of the water cycle.
How it works:
Plants suck up water (liquid) from the soil through their roots. They let extra water out through tiny, tiny holes in their leaves (called stomata). The liquid water evaporates and turns into invisible water vapour (gas), which floats away into the air.
💡 Fun Facts
- A large oak tree can release over 1,000 litres of water (that's more than 10 bathtubs full!) into the air in a single day.
- This is why rainforests are so damp and cloudy—the trees are all "sweating" and making their own clouds.
- This process also helps the plant to pull more water up from its roots, like sucking on a giant straw.
Why is the Grass Wet in the Morning?
Have you ever walked on grass early in the morning and your shoes get soaked, even when it hasn't rained? That's dew!
How it works:
The air all around us is full of invisible water vapour (gas). Overnight, the ground, leaves, and spider webs get cold. When the water vapour in the warmer air touches these
cold surfaces, it cools down and condenses. It turns from a gas back into little liquid water droplets that you can see.
💡 Fun Facts
- Dew is an important source of water for small insects and birds to drink.
- You get more dew on clear nights because the ground gets colder than on cloudy nights (clouds act like a blanket).
- Frost is just like dew, but it happens when the grass is so cold (below 0°C) that the water vapour freezes instantly into a solid!
The Desert Beetle's Drink
The Namib Desert beetle lives in one of the driest places on Earth. So, how does it get water? It "catches" it from the air!
How it works:
In the early morning, a cool fog blows in from the sea. The beetle climbs a sand dune and does a 'headstand'. Its back is bumpy and cool. The water vapour (gas) in the air hits its cool back and condenses into liquid water droplets. The droplets get bigger and bigger until they roll down the beetle's back, right into its mouth.
💡 Fun Facts
- The beetle's back has special waxy parts that the water slides off easily.
- This clever trick allows the beetle to drink in a place where it almost never rains.
- Scientists are copying the beetle's back to create new materials that can collect water from the air for people to drink.
The Water Cycle
The Water Cycle in the UK
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The water on Earth is constantly moving and changing state in a big loop called the water cycle.
- Evaporation: The sun heats up water in the sea, rivers, and lakes. The liquid water turns into invisible water vapour (gas) and rises.
- Condensation: High up in the sky, the air is colder. The water vapour cools down and turns back into tiny liquid water droplets, forming clouds.
- Precipitation: When the water droplets in the clouds get too heavy, they fall back to Earth as rain, hail, or snow.
- Collection: The water lands on the ground and flows into streams, rivers, and lakes, eventually making its way back to the sea, where the cycle starts all over again.
💡 Fun Facts
- The water you drink today is the same water that dinosaurs drank millions of years ago—it has just been recycled!
- The UK gets lots of rain because we are an island surrounded by the sea (lots of evaporation) and the air that blows over us is often cool (lots of condensation).
- It takes about 8 days for water to evaporate from the sea, form a cloud, and fall back as rain.
Activities & Reflections
Activities
Matter Detectives
Walk around the school grounds or classroom. List 5 solids, 3 liquids, and 1 gas you can find. (Example gas: air in a football, bubbles in a fizzy drink).
The Great Ice Melt Race
Put an ice cube in a few different places (e.g., in the sun, in the shade, on a metal tray, on a piece of fabric). Which one melts fastest? This shows how temperature affects the rate of melting.
Puddle Watch
After it rains, draw a chalk line around a puddle on the playground. Check it every hour. Does it get smaller? This is evaporation in action! Does it disappear faster in the sun or in the shade?
Steamy Mirrors
Get a small mirror and breathe on it. What happens? The invisible water vapour (gas) in your warm breath hits the cold mirror and condenses into tiny liquid water droplets, making it look steamy.
Reflections
Self-Reflection (Exit Ticket)
On a sticky note, draw a quick picture of the water cycle. Label where evaporation and condensation happen.
Paired Reflection (Think-Pair-Share)
Ask pupils to discuss with a partner: Is jelly a solid or a liquid? What about sand? (These are tricky ones to make them think about the properties of each state!)
Group Reflection
In small groups, discuss: Why does your wet PE kit dry faster on a hot, windy day than on a cold, still day?
Whole Class Share-Out
As a class, discuss: When you boil a kettle, you see 'steam' coming out of the spout. Is that 'steam' a liquid or a gas? (It's a mix! The hot, invisible gas—water vapour—shoots out and immediately cools, condensing into a visible cloud of tiny liquid water droplets.)
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