States of matter and why they matter

What do you observe? Remember that observations start with our senses, so something like “I see….”

When you start with “I think”, you are making an inference – a conclusion drawn from the data.

This image shows water in its various states of matter. Two states of matter are obvious – solid ice and liquid water. The third state is gaseous water vapour which is invisible.

This resource introduces common student alternative conceptions about changes and states of matter as they relate to water. It is important that teachers are aware of these during a sequence of lessons so students have a chance to begin changes in their thinking as the sequence progresses.

This video explains the nature of atoms or molecules in a solid state. Listen for what they’re doing – and what they can’t do.

Something is usually described as a solid if it can hold its own shape and is hard to compress or squash. The molecules in a solid are closely packed together – they have a high density. Right now, you are probably sitting on a chair or the floor and holding a pen or pencil – all of these things are solids.

In liquids, the molecules have the ability to move around and slide past each other. Think about taking a drink from a glass of water. The water molecules move easily from the glass to your mouth. Water takes on the shape of the glass until you tip the water into your mouth. Then the water takes on the shape of your mouth until you swallow it. While a liquid is easier to compress than a solid, it is still quite difficult – think about pushing on a syringe when it’s filled with liquid and you’ve blocked the end. You might be able to push it down a little, but not a lot.

In gases, the atoms or molecules are much more spread out than in solids or liquids, they’re able to vibrate more freely, and they collide randomly with one another. Gas can be compressed much more easily than a liquid or solid. Think about a helium tank that is used to blow up balloons. The Helium gas in the tank has been compressed, but it expands when it’s in the balloons – the total volume of the blown up balloons is much bigger than the volume of compressed gas in the helium tank.

Most people are familiar with three states of matter – solids, liquids and gases – but there are two more that are less commonly known but just as important – plasmas and Bose-Einstein condensates.

Plasma particles are also spread out and move around randomly, like in the gas state, but in a plasma there are free electrons, which gives plasma its ability to conduct electricity. If you don’t know what electrons are yet, don’t worry – they’re one of the components of atoms. Usually they’re moving as part of the atoms or molecules, but in plasma they can move even more freely, and because of this they release an electric charge.

Glaciers (awa kōpaka) are an example where water turns to ice and sometimes turns to water again.

Here’s a map of Aotearoa. Each of the red dots represents a glacier. Did you know that Aotearoa has over 3,100 known glaciers? Eighteen are on Mt Ruapehu and the rest are in Te Wai Pounamu – the South Island.

Glaciers form in places where snow falls year after year, and the layers of snow underneath are compressed and turn to ice. This takes a very, very long time – the ice in glaciers is made up of snow that fell hundreds or thousands of years ago.

We know ice is water in solid state, and it melts when heat energy causes the water molecules to move faster.

Now here’s a question: Does ice melt faster in water or in air?

This experiment is modelling what happens when glaciers melt.

Scientists often use models to represent something that we cannot experience directly - in the case of glaciers melting, models are used because the actual time frames for glaciers to melt is tens or hundreds of years.

In this activity, students develop a concept map to summarise current ideas about states of matter.

You could try doing this activity as a collaboration.