# Transcript

Narrator
This animation illustrates how water molecules behave under normal conditions, for example, in a glass of pure drinking water. The water molecules are in constant random motion, bumping into each other and bouncing apart.
This way of representing water molecules is called a space-filling model because filled spheres are used to represent the atoms. Each water molecule is represented by three overlapping spheres, a single large red sphere, representing an oxygen atom, which is joined to two small white spheres, the two hydrogen atoms in a water molecule. Oxygen and hydrogen are two of the more than 100 unique chemical elements known to science.
Of course, water molecules are not really made of overlapping red and white spheres. The colours chosen for the atoms are simply a convention in chemistry. Oxygen atoms in molecular models like this one are always coloured red, and hydrogen atoms are white.
A static image makes it easier to describe the structure of an individual water molecule. In the space-filling model of a water molecule, the single oxygen atom is red and is joined to two hydrogen atoms coloured white. Here the hydrogen and oxygen atoms have been labeled with their chemical symbols, capital H for hydrogen and capital O for oxygen. Combining these symbols gives the familiar chemical formula for water, H2O. Water is described as a chemical compound, because the water molecule contains more than one type of atom.