Helping Students Learn the Particle Theory:

1. Using models to 'visualise' the world

2. Understanding the abstract idea of the particle nature of matter
- Teachers should be alert of the ideas commonly held by students.
- A variety of phenomena should be presented to reinforce student learning.
- Should guide students to interpret and reason.
- Should provide practices in using scientific ideas.
- Should ask students to demonstrate the use of knowledge.


Science is about explanation. It attempts to make sense of the world by constructing models or theories through a creative approach. This Unit on "Matter as particles" is difficult for students because they are being introduced to a model scientists use to explain the behaviour of matter and the abstract idea that all matter is particulate in nature.

1. Using models to 'visualise' the world
The model introduced at this level is very simple. The kinetic motion model with ball bearings being energized and bounced around by a vibrator in a tube is very helpful in explaining changes in state and pressure/volume relationships. Once shown this, students can apply the understanding of the model to explain not only evaporation but also why water at 70oC will evaporate more quickly than water at 50oC. They can also explain why evaporation will occur more rapidly on a windy day or why blowing on a cup of tea will cool it. However, students will find that there are other phenomena that cannot be fully explained using the model they have learned. For example, if students are asked to investigate phenomena related to solubility. They will find that "substances will dissolve more quickly in hot water because the water particles in hot water have more energy and will jiggle around more quickly knocking into the solid so making it dissolve". But they may not be able to "explain why the solubilities of different substances vary considerably" and why some substances do not appear to dissolve in water. More sophisticated models are required. To help students to appreciate how scientists use models in explaining the world and to ensure that students practice in using models to explain phenomena and to see the limitations of models, the following teaching strategy can be employed:

  • Teach the model, making sure students understand it and that they can 'picture' it.
  • Show students how the model can be used to explain certain phenomena
  • Practice using the model e.g. introduce a new phenomenon and ask students to use the model to explain it
  • Challenge the model - perhaps through an investigation. Encourage students to see the limitations of the model by asking them to explain new phenomena which cannot be explained with the model
  • Teach a more sophisticated model as appropriate

2. Understanding the abstract idea of the particle nature of matter
Teachers should be alert of the ideas commonly held by students.

To help students learn important ideas about the particle theory, teachers should be aware of the ideas commonly held by students. Students' ideas and interpretations related to Matter and Particles are a natural result of their everyday experiences and should be properly addressed before the taught theory could really sink in. (Reference: Children's Learning in Science Project: Aspects of Secondary Students' Understanding of the Particulate Nature of Matter by Angela Brook, Hazel Briggs & Rosalind Driver - January 1984)

The following example states a misconception, explains it, explains why students believe it, and describes what has to change for them to find the scientific idea that particles are perpetually in motion credible.

Students have difficulty in understanding that particles are constantly moving. Particles are always moving, even in substances such as ice where no motion of the substance is visible. Many students think that particles are moving in liquid water because liquid water is flowing, but particles are not moving in ice because ice is not moving. The constant motion of particles is difficult for students to believe, both because it seems to contradict the evidence of their senses and because they have never encountered objects that, like particles, are so tiny that they are unaffected by friction and thus never come to a stop.

A variety of phenomena should be presented to reinforce student learning.
A phenomenon is an event that can be scientifically described. Much of the point of science is explaining phenomena in terms of a small number of principles or ideas. For students to appreciate this explanatory power, they need to have a sense of the range of phenomena that science can explain. For example, to make the idea plausible that "particles in matter are perpetually in motion, the following examples could be presented to the students:

  • When air is compressed in a syringe, it pushes back on the plunger
  • Gases (like perfume) spread out evenly in a room or container ?
  • Liquids (like food coloring or tea) spread out evenly in a glass, rather than falling to the bottom
  • Solids like gold and lead can mix a bit, but it takes considerably longer to observe

But experiences with phenomena are not enough! Students need help to understand and appreciate how the phenomena relate to the scientific ideas.

Should guide students to interpret and reason
For example, after students see that air can be compressed in a plastic syringe and read about the large amount of air that can be compressed in a small scuba tank, questions guiding students to think about the phenomena should be included. The question below probes the common student misconception that particles are not perpetually in motion:

John says, "there is more air near the valve of the bike tire where the air was pumped in." Do you agree with him? Explain why or why not.

In another lesson, students observe that even though sugar grains appear (with magnifying glass) too big to get through a presweetened tea bag, the sweet taste does indeed "get out." They try to explain how the sugar might have gotten out.
Did you say that you could see wavy lines under the tea bag and taste the sugar in the water? That is true. We cannot see the tiny particles of sugar or the tiny particles of water; but we can taste the sugar in the water. The sugar did not disappear forever, but the sugar grains broke into separate, tiny particles, so that we could no longer see the sugar. Just because we cannot see the sugar does not mean it is not there. The water tastes sweet, so it must still be there.

How did the sugar get out of the tea bag? The holes in the tea bag are much smaller than a grain of sugar, but much larger than a particle of sugar. As the water particles hit the solid sugar, the particles of sugar break away rapidly and mix with the water particles. The tiny particles easily pass through the holes in the tea bag.

Finally, students are asked a question that anticipates a common misconception (that particles are not perpetually in motion but only move if the substance appears to move):

If you let this cup stand overnight, would the sugar rise to the top, settle to the bottom, or spread evenly throughout the water? Talk about particles to explain your answer.

Once an idea begins to take hold, students need many and varied opportunities to apply it.

Should provide practices in using scientific ideas.
Students should be provided with a sufficient number and variety of practice tasks for most of the ideas examined around the particle theory. These include novel tasks that ask students to develop descriptions and explanations of phenomena they see all around them. Since explaining real world phenomena often requires using more than a single idea, the phenomena students are asked to explain should increase in complexity. For example, the following questions required students to move from using mainly the idea that "particles are in perpetual motion" to using this and related ideas:

  • Draw pictures to show how water particles are moving.
  • Can water particles in ice slow down and stop?
  • If you want something to dissolve fast, should you mix it with hot water or cold water? Why?
  • Explain how you can smell an open bottle of vinegar even though you are across the room. What is actually reaching your nose? How did the vinegar particles get into the air? How did the vinegar particles reach your nose?
  • When food covered with plastic wrap in the refrigerator (or when soup is warming on the stove, but not boiling, with a lid on the pot), water evaporates and then condenses. Where does the water evaporate from? Where does the water condense? How do the water particles get from the place where water evaporates to the place where water condenses?

Should ask students to demonstrate the use of knowledge.
Teachers should first show students how to explain phenomena and then coach them through a few explanations before turning them loose to explain how the world works. Teachers should first announce that they are beginning the demonstration, then provide a step-by-step demonstration, and finally provide criteria for judging the quality of the explanation. For example:

How does evaporation happen? Let's try explaining it in terms of particles. You know that the particles in liquid water are constantly moving. In a liquid, though, the attractive forces between particles keep them close together. What you might not know is that the particles in a liquid move at different speeds. Some particles are moving very fast, while other particles are moving more slowly.

What do you think would happen if a fast-moving particle reached the surface of a drop of water? Yes, it would escape! It would break away from the strong attraction of the other water particles and become a particle of water vapor in the air. If all the water particles escape in this way, we say that something has "dried out." The liquid water has turned into water vapor in the air, and the water vapor makes the air more humid. You have also learned something about scientific explanations. To make a good explanation, you often need to talk about particles.

You need to talk about the way particles move and the way they are arranged in solids, liquids, and gases. You also need to know what kind of particles you are talking about. You need to identify the substance that is changing and tell how it is changing. In other words, a good explanation answers at least two questions:
A question about substances: What substance is changing and how is it changing?
A question about particles: What is happening to the particles of the substance?

When students first begin to practice explaining phenomena, they are reminded of the criteria and asked whether their explanations meet them. As students proceed through the unit, they are reminded less often until they are explaining on their own.

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