As particles cannot be directly observed, much of the teaching involves looking for apparent problems or inadequacies with the sorts of static pictures of particles given in earlier years.
Encourage students to identify these and talk through possible explanations. Some prompts:. If needed, raise issues such as these, which will open up discussion, but it is better if the students themselves come up with some.
Note that many of the issues are to do with gases — it is their properties that we most need a particulate model to explain. To reinforce the notion of elastic collisions, ask what would happen if collisions between gas particles were not elastic.
What practical consequences would there be for people? This can be introduced by dropping different types of balls such as a soccer ball, a table tennis ball and a bouncy ball from toy shops and explaining that a bouncy ball behaves more like gas particles.
Using activities like POE Predict-Observe-Explain can help students think about and then question their existing ideas. The following activity will help students consider their ideas about the movement of particles. Set up two pairs of flasks each connected by a valve see diagrams below. Both pairs have brown nitrogen dioxide in the left hand side flask. The first pair also has air in the right hand side flask.
Students are asked to predict what will happen when the valve between the two flasks is opened. The brown colour will spread very slowly from one flask to the other because the particles have frequent collisions with the air particles. The second pair of flasks has brown gas in the left hand side flask but the right hand side flask is completely evacuated.
Students are asked again to predict what happens when the valve is opened. The very fast speed of the molecules means that they fill the evacuated flask very quickly. Diffusion experiments can reinforce the idea of movement of particles. These can also be used as POEs.
Brownian motion can also be observed using stereo microscopes when sulphur powder or camphor is sprinkled on the surface of water or ethanol.
A cotton wool piece soaked in ammonia is placed at one end of a long glass tube with another soaked in hydrochloric acid HCl placed at the other end. Eventually a white ring will form where the two gases meet. The two gases are at the same temperature and thus the particles have the same kinetic energy; the ring forms closer to the source of heavier and thus slower moving HCl.
This is predicted by a comparison of the relative molecular masses. Including a strip of universal indicator paper in the tube allows the gas diffusion to be tracked.
Students need to be given the opportunity to use the scientific conceptions about particle theory in other settings. Molecules within gases are further apart and weakly attracted to each other. Heat causes the molecules to move faster, heat energy is converted to kinetic energy which means that the volume of a gas increases more than the volume of a solid or liquid. However, gases that are contained in a fixed volume cannot expand - and so increases in temperature result in increases in pressure.
Ignoring rotation is fine for me but can you explain the vibration of gas molecules? I thought they didn't vibrate by themselves without colliding others since they are not connected unlike liquid and solids molecules. All molecules vibrate: the distance between the atoms in the molecule oscillates like a spring. Also see en. When I was thinking about molecules, I forgot to think about atoms in them. Of-course they vibrate : Can we say an hydrogen atom also vibrates by itself without colliding anything else?
Maybe because interaction between the proton and electron or maybe the interaction between quarks? See physics. Quark vibrations should exist within a proton, but a proton is a very messy system because of the self-interaction of gluons. Featured on Meta. Now live: A fully responsive profile. Linked Related 6. Hot Network Questions.
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