A compound is a substance that is made of two or more elements that are chemically joined. You cannot separate the elements without breaking the chemical bonds.

Take water for example. Water is made of atoms of two elements: Hydrogen (H) and Oxygen (O). Two Hydrogen atoms bond with one Oxygen atom to form a molecule of water.

Molecules of water look the same no matter what state the water is in; liquid, solid (ice), or gas (water vapor).