Water is made up of Hydrogen and Oxygen. Hydrogen and Oxygen are called elements. Elements are the building blocks of all matter, and cannot be broken down further into other substances.

Each element is a different kind of atom. The element “Hydrogen” is made of a Hydrogen atom. The element “Oxygen” is made of an Oxygen atom.

Atoms of different types join together to make matter. For example, Hydrogen and Oxygen join together to make water. To make water, two Hydrogen atoms join with one Oxygen atom. When they join together, they make a molecule of water.

Molecules are made up of atoms that are joined together chemically. Millions of molecules of water make up a cup of water that you drink.

The illustration at the right shows some common molecules and the atoms that they are made from.