Atoms join up

About this video

Look at a glass of water. Everything is made of atoms, and an element is made of only one kind of atom. But water is not an element: you won't find it on the periodic table. So what is water made of?

The answer is that atoms can join up. Two or more atoms can hold on to each other and stay together. A small group of atoms joined together is called a molecule. Water is made of tiny molecules, all exactly alike, and each one is two hydrogen atoms and one oxygen atom: the oxygen in the middle, a hydrogen on each side, a bit like the ears on a head. In pictures like these oxygen is red and hydrogen white, but atoms aren't really coloured balls, and nothing here is to scale: a real water molecule is far too small to see with any magnifying glass.

When water boils, the molecules fly apart from each other, but each molecule stays whole. Steam is still made of water molecules.

A molecule can also be made of atoms of one element. The oxygen in the air goes around in pairs: two oxygen atoms joined into one oxygen molecule. Nitrogen, most of the air, goes in pairs too. Not every atom joins up into small groups, though: the helium in a party balloon is single atoms, each on its own. Why atoms hold on to each other at all is a story for a later level.

Transcript

1. 0:00Water isn't on the periodic table. So what is it made of?
2. 0:07Zoom in billions of times, and water is tiny groups of atoms, all alike.
3. 0:16One oxygen atom, two hydrogen atoms, joined up. That is a water molecule.
4. 0:25When water boils, the molecules fly apart, but each one stays whole.
5. 0:33Air is pairs of nitrogen and pairs of oxygen. Helium is single atoms.
6. 0:42A molecule is a small group of atoms joined together.