What is matter made of?

What is matter?

Everything around you is made of something. A table, a cup, the water in it, the air in the room, and your own body are all made of matter.

Matter is anything that has mass and takes up space. Mass is how much matter an object has. Space is the volume that it fills.

Is a smell matter? A smell comes from a substance that spreads in the air, so yes. Is light matter? No, it has no mass and takes up no space. Is a thought matter? No. Is air matter? Yes. We cannot see it, but a balloon with air in it is heavier than a balloon with no air, and the balloon fills with air and takes up space.

A good test has two questions: does it have mass? and does it take up space? Only if both answers are yes is it matter. A stone, water, steam, air and a spark of fire (the hot glowing gas) are matter. Sound, heat, light, a shadow and a thought are not matter.

Is matter smooth or in pieces?

Is a block of salt one solid piece, with no gaps? Or is it made of many tiny pieces? Scientists have found that matter is made of particles, which are very small. We will find some facts that show this.

The idea is old. About 2500 years ago, two thinkers had the same idea: Kanada in India and Democritus in Greece. Keep cutting a piece of matter, they said, and you reach a smallest piece that cannot be cut again. Today we know that matter is made of atoms and molecules, and the experiments below let you see, with simple things, that this is a good idea.

Experiment 1: how small is a particle?

Dissolve two or three small crystals of potassium permanganate in a glass of water. The water becomes purple. Now take a little of this purple water and add it to a larger glass of clear water. The water in the larger glass is still coloured, though a lighter purple. Do this again and again. After many times, the water is still a little coloured.

A few crystals can colour a very large amount of water. So each crystal must contain a very large number of particles, and each particle must be very small. The particles of matter are too small to see even with a microscope.

You should find that ten dilutions make the colour ten thousand million times weaker, and a drop still holds a huge number of particles.

To get a feel for the numbers: a single drop of water holds about $1.7 \times 10^{21}$ molecules. That is a number with 22 digits. And a molecule of water is about $0.3$ billionths of a metre across.

Experiment 2: spaces between the particles

Take a glass half full of water, and mark the level. Now dissolve a spoon of sugar in it. The level does not rise. Where did the sugar go?

The particles of sugar went into the spaces between the particles of water. So there are spaces between the particles of matter. In the same way, a spoon of salt dissolves in water without changing the level much.

Think of a bucket filled with marbles. It looks full. But you can still pour in a cup of sand, which goes into the gaps between the marbles. The level hardly changes. Sugar in water is like sand among marbles.

Air shows the same idea. A large amount of air can be squeezed into a small cylinder, because the particles of air are far apart and can be pushed close together. A bicycle pump does this. The air in a tyre is squeezed to a fraction of its size.

Putting it together

Practise with new numbers

Try it in Python

The program follows the particles of a crystal of potassium permanganate through eight dilutions.

Common mistakes

• Thinking that matter is "solid all through". Even a solid block has spaces between its particles, though they are very small.
• Thinking that the particles are the same as the pieces that you can see. A grain of sugar holds millions of millions of particles.
• Calling air "nothing". Air is matter. It has mass and takes up space.
• Thinking that light and sound are matter. They have no mass and take up no space.

Remember these

• Matter is anything that has mass and takes up space.
• Matter is made of particles. They are very small, too small to see even with a microscope.
• There are spaces between the particles of matter.
• Gases have the largest spaces, so they can be squeezed.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Is the smoke from a candle matter? Is the light of the candle matter? Give a reason for each.

2. A glass is filled to the brim with water. A spoon of sugar is stirred in slowly, and no water spills. Explain.

3. A coloured solution is diluted five times, each time $10\ \text{mL}$ into $90\ \text{mL}$ of clear water. How many times weaker is the colour? What does this tell you?

4. Why can a lot of air be pumped into a car tyre, but a full bottle of water cannot take in more water?