A ball and stick model can be used to show the structure of a simple molecule. This type of model has the advantage of showing how the atoms are connected and how they are arranged in space, including the angles between bonds.
An alternative 3D model, often used in computer simulations, is a space-filled model. This has the disadvantage that it is no longer possible to see the angles between bonds. The main advantage is that it shows the overlap of the electron shells of the atoms.
You can represent a simple molecule by drawing its structure. In these structures:
For example, a hydrogen molecule has two H atoms and one covalent bond. The diagram shows its structure.
A carbon dioxide molecule has one carbon atom that is connected to two oxygen atoms via double bonds.
The advantage of a displayed formula, compared with a molecular formula, is that it shows how the atoms are connected. The disadvantage is that it does not show how the atoms are arranged in 3D space.