The three states of matter are a core principle of chemistry. They feature in a range of topics on the GCSE curriculum, from particles to changes of state. Matter refers to anything that has mass and takes up space. Most things we see in the world around us are made of matter, whether they are a solid, liquid, or gas. The differences in state are caused by the particles being arranged and moving in different ways.
This article will explore each state of matter and its unique properties. We will show how matters can change state in the right circumstances, such as melting from a solid to a liquid, boiling from a liquid to a gas, and condensation, when a gas turns back into a liquid. Each topic is explained in relation to particle theory. It is suitable for GCSE Chemistry students revising for their examinations.
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What Is Matter?
Matter is anything that has mass and takes up space. This means effectively everything we see around us is matter. The laptop or phone you are reading this article on, a book you're reading, the bed, sofa, or chair you're sitting on. Even the clouds in the sky and the air in the room. Anything that occupies space and can be weighed is made of matter.
These are a few examples:
- A brick - This is a solid and heavy
- Water - This is a liquid, yet it still has mass
- Oxygen - This is a gas. We can't see it, but it can fill a container and be measured
- Light and sound - This is not matter. It doesn't have mass and doesn't take up space
Matter is made from particles (atoms and molecules). They are tiny and invisible to the naked eye. They are always moving, either vibrating, sliding past each other, or spreading out. The differences in their movement help us explain why materials behave differently in different states.
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Which is not a type of matter?
Different States of Matter - Solids
A solid has a fixed shape and volume. It keeps the same form and won't change if you move it from one place to another. The only way a solid can be changed is if it's cut, broken, or changed in some other way. It is a state of matter that has a fixed shape and a fixed volume. Examples include a ruler, a brick, a pencil and an ice cube.
The particles are packed closely together in a regular pattern. They vibrate on the spot because they don't have enough energy or space to move freely. A solid is hard to compress because the particles are so close together. This arrangement of particles explains why a solid feels firm and keeps its structure.
If you heat a solid, the particles have more energy. This causes them to vibrate faster and will eventually cause them to melt into a liquid, changing the state of matter. For example, ice turns into water when the temperature rises. This transition affects how the particles are arranged and how they move.
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Why are solids hard to compress?
Liquids
A liquid has a fixed volume but not a fixed shape. Its shape is determined by the container it is placed in. For example, water poured into a tall glass will take the appearance of the glass, becoming tall and narrow. Similarly, water poured into a bowl will spread out. The amount of liquid is a constant, but the shape changes.
The particles are close together, but they aren't arranged in a fixed pattern. They have more energy and freedom to move, sliding past each other. This is how liquids can flow and be poured. A liquid is also hard to compress because the particles are still quite close to each other, making it difficult to squeeze into a smaller space.
The particles gain energy and move faster when heated. This eventually causes particles to escape the surface and turn into a gas, a process known as evaporation. This occurs frequently, even at room temperature. When the liquid reaches its boiling point, bubbles of gas start to appear through the liquid, such as when you turn the kettle on.
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What is the correct description of particles in a liquid?
Gases
A gas has no fixed shape or fixed volume. It spreads out to fill the available space. The gas won't be in a corner of the room. Instead, it spreads across the room until it is evenly distributed. This is why smells travel through the air quickly.
The particles are much further apart. This means they have more energy and can move very quickly in any direction. A gas is easy to compress because of the empty space. For example, if you pump air into a car tyre, the particles are pushed closer and closer together, increasing the pressure.
When you heat a gas, the increased energy causes the particles to move even faster. They collide with the walls of their container more frequently and forcefully. This is why a party balloon expands when it is warmed.
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How do particles behave in a gas?
Changing states of matter
When a substance gains or loses energy, it can change state, such as from a solid to a liquid. This is normally in the form of heat. The particles don't change - rather, they are arranged and move differently. We have listed the main types of change you need to know for GCSE Chemistry.
Solid to liquid - Melting
If you heat a solid, the particles gain energy and vibrate more. This increased vibration eventually weakens the forces keeping them in a fixed position. It begins to melt, turning into a liquid. The common example is an ice cube melting into water. When this happens, the temperature remains the same until the solid has fully changed to a liquid.
Liquid to solid - Freezing
If you cool a liquid, you are removing energy, such as putting a bottle of water in the freezer on a hot day. The particles lose energy and move more slowly. This causes them to move closer together and arrange into a fixed pattern, turning the liquid into a solid. Freezing a liquid back into a solid is the reverse of melting. The temperature stays constant while the change happens.
Liquid to gas - Boiling and evaporation
Particles move quickly when a liquid is heated. Eventually, some particles will escape the surface - this is called evaporation. Bubbles of gas form throughout the liquid when the liquid reaches its boiling point. A common example is water boiling into steam when cooking or boiling the kettle.
Gas to liquid - Condensation
If a gas is cooled, the particles lose energy and move more slowly. They compact together and turn into a liquid. This is known as condensation, such as when you see droplets on the rim of a cold drink, or when steam turns back into water on a bathroom mirror after a hot shower.
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What happens when a solid melts?
Bose-Einstein condensate (BEC) and Plasma
The GCSE curriculum focuses on the three main states of matter: solid, liquid and gas. Other states aren't required for GCSE Chemistry. Two of these are Plasma and the Bose-Einstein condensate. We have explored them briefly to give you an overview.
Plasma
Plasma is considered a fourth state of matter. When a gas is heated to a very high temperature, the particles have enough energy to break apart. The gas becomes a mixture of positive ions and free electrons. The particles are now charged, which means the plasma can conduct electricity and respond to magnetic fields.
Plasma is very common in nature and the universe. Stars are composed almost entirely of plasma. Lightning is another example. It's also common in technology, such as plasma TVs and some cutting and welding equipment.
Bose-Einstein condensate (BEC)
The Bose–Einstein condensate is an unusual state of matter, also called BEC. It only forms at very low temperatures, just above absolute zero (?273 °C). The particles lose almost all their energy and behave like a single, shared particle.
In a BEC, the particles overlap and act together. This gives the material unusual properties, such as flowing without resistance. It was created in 1995 by scientists in a laboratory. They cooled rubidium atoms with lasers and magnetic traps.
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What is special about a Bose-Einstein condensate?
Final thoughts - Three states of matter
The three states of matter are an example of the relevance of chemistry. They explain a great deal of the world around us. Solids hold their shape, liquids flow and adopt the shape of their container, and gases spread out to fill the available space. When answering questions on this topic, always relate the matter and changes of state to how particles move and energy changes. Even more unusual states, such as Bose-Einstein condensates, show that scientists are still uncovering new ideas about how matter behaves under extreme conditions.
For further reading, Wikipedia has an article on plasma as the fourth state of matter. You can also test your understanding with these past paper questions on states of matter by Physics and Maths tutor.
If you’d need extra help revising this topic, TeachTutti has qualified GCSE Chemistry tutors who can provide personalised support, such as preparing revision notes.
This post was updated on 30 Nov, -0001.
