Answer is: scientists use different types of model to show different characteristics (chemical properties) of compound.
For example, ball and stick model gives informations about bond lenght and space filling model gives information about space occupied by atoms.
In chemistry, the ball-and-stick model is a molecular model of a chemical substance which is to display both the three-dimensional position of the atoms and the bonds between them. The atoms are represented by spheres, connected by rods which represent the bonds. Every ball represent one atom in one molecule and they have different colors for different atoms (for example, carbon is black, hydrogen is white, nitrogen is blue).
There also other models: skeletal models, polyhedral models, composite models, computer-based models.
