In this lesson we will learn about the three main states of matter and the properties that characterise them.
By the end of this lesson you will be able to:
Describe properties of solids, liquids and gases.
Describe the different states of water.
States of Matter
- Previously in science you learned that matter is anything that has mass and takes up space.
- Not only does matter come in many different forms, but it can also exist in three main states, known as solid, liquid and gas.
- In these different states, the same substance exhibits different physical properties.
- The main ways that solids, liquids and gases differ are their shape, compressibility and density.
Solids, liquids and gases have different properties.
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- If an ice cube is taken out of a freezer and placed in a glass, it still has the same shape as when it was in the ice tray.
- Its shape doesn’t change.
- We can therefore say that solids have a fixed shape.
Solids, such as ice cubes, have a fixed shape.
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- If water is poured into a glass, the water takes on the shape of the glass. If the water is then poured from the glass to an ice tray, it takes on the shape of the ice tray.
- Its shape changes, depending on the shape of the container it is in.
- We can therefore say that liquids have a variable shape.
The shape of liquids changes, depending on what they are in.
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- Although we can’t see water vapour, or most other gases, we can determine their shape.
- For example, if a balloon is filled with helium gas (the type of gas that makes party balloons rise into the air), the gas takes on the shape of the balloon, which might be round, star-shaped or heart-shaped.
- We can therefore say that gases have a variable shape.
The shape of gases changes, depending on what they are in.
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Volume and Compressibility
- Volume refers to the amount of space something occupies.
- Compressibility refers to whether a substance can be forced to occupy a smaller volume.
- Imagine if you could change the shape of a solid by squishing it (think of plasticine, for example). Regardless of what shape you made it, and regardless of how hard you squished it, you couldn’t make the plasticine take up less space.
- We can therefore say that solids have a fixed volume.
- In other words, solids cannot be compressed to take up less space.
Bricks would be less useful if they could be squashed and made smaller.
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- Imagine a water balloon that doesn’t burst when you squish it. Similar to the plasticine example, regardless of how hard you squished it, you couldn’t make the water balloon take up less space.
- We can therefore say that liquids have a fixed volume.
- In other words, liquids cannot be compressed to take up less space.
Hydraulics, as seen here on this excavator, utilises the incompressibility of liquids.
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- Imagine you are in a room and at the other end of the room there is an LPG gas bottle. If the gas bottle starts to leak, you will eventually smell the gas, regardless of where you are in the room.
- This is because the gas that escaped from the bottle has expanded to fill the room. This is the opposite process to that which took place when the gas was forced into the bottle when it was filled.
- We can therefore say that gases have a variable volume.
- In other words, gases can be compressed to take up less space.
Scuba tanks contain compressed air, which allows divers to breathe under water.
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- Density refers to how heavy something is relative to its volume.
- Imagine a block of concrete (a solid), a bucket of water (a liquid) and a balloon (representing the gas inside the balloon), all of which are the same size (volume). The block of concrete and bucket of water would be quite heavy, but the balloon would be very light. We can therefore say that the concrete and water have high density whereas the air has a very low density.
Density refers to how heavy something is, relative to the amount of space it takes up.
- Solids have a high or very high density (are ‘heavy’ or ‘very heavy’).
- The density of solids can vary.
- For example, most metals are much denser than ice. A block of iron the same size as a block of ice would be almost eight times heavier.
- Some solids, such as styrofoam, may appear very light, but these mostly consist of pockets of air, which is a gas.
Solids have a high density.
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- Liquids have a high density (are ‘heavy’).
- Similar to solids, the density of liquids can vary, but not as widely.
Liquids have a high density.
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- Gases have a very low density (are ‘very light’).
- Gases can have different densities, but all are very light compared to liquids and solids.
Gases have a very low density.
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The Different States of Water
- Water is a unique substance because it exists in all three states in different parts of the earth.
- In most places, water exists as a liquid. For example, as rain, in rivers and oceans, and as groundwater.
- At the north and south poles, and in many mountainous regions, water exists as a solid, which we call ice.
- Perhaps less obviously, water also exists in the air around us, as a gas, known as water vapour.
- We cannot see water vapour because it is invisible, but we can often feel its effects, especially in humid areas like the tropics, where we might describe the air as feeling ‘humid’, ‘sticky’ or ‘muggy’.
- Humidity is a measure of how much water, in the form of water vapour, is in the air.
- Like water, most substances can exist in three states.
- For example, the metal iron is normally a solid. You may have seen pictures of molten iron, for example, in a furnace – this is iron in liquid form. But did you know that iron can also exist as a gas? (In the next lesson we will look at how this is possible.)
Water exists in all three states on Earth.
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- Matter can exist in three different states: solid, liquid and gas.
- Solids, liquids and gases have unique properties that characterise them.
- The properties of solids are:
- • Fixed shape.
- • Fixed volume.
- • Not easily compressed.
- • High or very high density.
- The properties of liquids are:
- • Variable shape.
- • Fixed volume.
- • Not easily compressed.
- • High density.
- The properties of gases are:
- • Variable shape.
- • Variable volume.
- • Easily compressed.
- • Very low density.
- Water exists naturally on Earth in all three states – as ice, liquid water and water vapour.
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