Matter that has only one kind of atom is called an element. Gold, copper, oxygen, and mercury are examples of elements. Most matter is made up of two or more different kinds of atoms that are chemically combined. This kind of matter is called a compound.
Solids, liquids, and gases are made of tiny particles called atoms and molecules. In a solid, the particles are very attracted to each other. They are close together and vibrate in position but don't move past one another. In a liquid, the particles are attracted to each other but not as much as they are in a solid.
