The simple particle model pictures particles as small, hard, inelastic spheres, like tiny bowling balls. This works well to show the arrangement of particles in solids, liquids and gases and to explain changes of state. However, like any model, it has limitations.
First, the model does not take into account the forces of attraction between particles. Bowling balls do not pull on each other, but real particles do. These forces are what hold a solid together and are why different substances have different melting points and boiling points. Second, the spheres are all drawn the same size, so the model ignores the real size of particles, which differs between substances: particles have different sizes. Third, it does not show the space between particles correctly. The spheres touch in a solid, but in a gas the space between particles is mostly empty and much larger than the particles.
The model also treats particles as solid objects that do not change shape. Real particles can be made of several atoms joined together, and can have complicated shapes. Because of these limitations, the model cannot explain why different materials have different properties, or why they melt and boil at different temperatures.