The particle model is very useful in helping explain many chemical reactions, but there are times when the model works less well.
Chemistry uses models to try to explain what is happening during chemical and physical changes. However, these models are simple. This means that there are limits to how far models can show exactly what is happening in reactions.
For example, potassium and calcium are next to each other in the periodic table. They are both metals and are both solids. Potassium melts at 64°C, but calcium melts at 842°C, so the particles behave differently in the two elements.
The particle theory assumes that particles are the same in all substances. However, particles in real life may be different from element to element in the following ways:
One other factor that is important is the type of interactions between particles. The kinetic theory model assumes that particles collide and bounce off each other. But, in reality, particles often do not simply bounce off each other because they have forces of attraction between them. This affects properties such as melting point. One example of this variation can be seen with CO2 and SiO2. These are both oxides of elements in group 4 of the periodic table. However, carbon dioxide (CO2) is a gas and silicon dioxide (SiO2) is a solid - the particles behave in different ways because of their mass and the forces between them.