Molecules

📖 In short

A molecule is a tiny group of atoms joined together. It's the smallest piece of a substance that still has its properties. A water molecule, for example, is made of two hydrogen atoms and one oxygen atom, and we write it H₂O.

🤩 Did you know?

The formula for a water molecule is H₂O.
A carbon dioxide molecule has a mass of about 44, because it has one carbon atom and two oxygen atoms.
The DNA in your cells is a very long molecule that carries your traits.
Molecules can be broken apart by strong radiation or heat.

🔎 Find out more

🌟 Like building blocks

Imagine atoms as colorful building-toy pieces, and molecules as the shapes we make with them. With just a few kinds of pieces we can make a huge number of shapes, and that's how all substances are formed.

🔍 Small and large molecules

Some molecules are tiny, with two or three atoms, like oxygen and water molecules. Others are huge, with thousands of atoms, like protein, sugar and plastic molecules.

💡 What if we split it?

If we split a water molecule, it isn't water any more but hydrogen and oxygen atoms, gases completely different from water!

🎯 Molecules move

Molecules are always moving. Put a drop of ink in a glass of still water and wait: the ink spreads through all the water by itself, because the water molecules move and push it.

🧩 Test yourself

1 What is a water molecule made of?

2 What happens to a drop of ink in a glass of water?

3 A carbon dioxide molecule has a mass of about ?? , because it has one carbon atom and two oxygen atoms.

4 Which picture shows “Molecules”?