Developing an understanding of particle theory

Transcription

1 The National Strategies Secondary Developing an understanding of particle theory 1 For pupils to understand the particle theory properly we need to: teach a simple model challenge pupils to use the model to explain what they observe. The yearly learning objectives require that pupils are explicitly taught a simple model of particle theory in. They are then expected to use this model to explain a range of phenomena. pupils should be challenged to use their developing understanding to explain things they observe. This may require a change in the way we teach and question pupils. When pupils encounter the phenomenon of expansion we need to be asking questions such as what do you know about particles that can help us explain why heating has led to expansion? Reflection Look at this extract from the yearly learning objectives for How science works. This extract is from the substrand 1.1a1, Scientific thinking: developing explanations using ideas and models. 1.1a1 Scientific thinking: developing explanations using ideas and models use an existing model or analogy to explain a phenomenon recognise and explain the value of using models and analogies to clarify explanations describe more than one model to explain the same phenomenon and discuss the strengths and weaknesses of each model describe how the use of a particular model or analogy supports an explanation describe the strengths and weaknesses of a range of available models and select the most appropriate explain why the manipulation of a model or analogy might be needed to clarify an explanation justify the selection of a particular model as the most appropriate devise own simple models or analogies to explain observations, data or scientific ideas evaluate the effectiveness of using models and analogies in their explanations evaluate the strengths and weaknesses of their own models and analogies recognise that it is possible to have and to use different, and sometimes conflicting, models in their explanation explain how devising and using alternative models could help to make a creative leap in an explanation Crown copyright PDF-EN-13

2 2 The National Strategies Secondary You should be able to identify: that the learning about models begins specifically in where the learning develops progressively across the five years how the learner is expected to use, apply and evaluate models, not just remember, draw or represent them that the learner may need to adapt or replace a model with a more appropriate one. Now look at these yearly learning objectives from Chemical and material behaviour Chemical and material behaviour 3.1 Particle models describe matter using a simple model and use it to explain changes of state recognise the link between heating and cooling and changes of state use the simple particle model to explain the physical characteristics of solids, liquids and gases apply and use the particle model to describe a range of physical observations apply and use the particle model to describe a range of separation techniques evaluate and refine the particle model to explain a range of physical observations evaluate and refine the particle model to explain a range of separation techniques apply particle models in unfamiliar contexts, and begin to evaluate the strengths and weaknesses of the model refine the particle model to explore the structure of atoms, including protons, neutrons and electrons use the particle model and ideas from science and across disciplines to explain phenomena and evaluate the use of the model use the particle model and ideas from science and across disciplines to explain complex phenomena and make critical evaluations to justify the use of a good enough model PDF-EN-13 Crown copyright 2009

3 The National Strategies Secondary 3 Chemical and material behaviour 3.2 Chemical reactions sort some reactions into reversible and irreversible recognise that new materials are made during chemical reactions recognise that materials can be made up of one or more kinds of particles describe the type and arrangement of atoms in elements, compounds and mixtures describe and develop a particle model to explain the differences between the terms atoms, elements, compounds and mixtures use a particle model to construct predictions for simple chemical reactions and to produce word equations use a particle model to construct predictions for chemical reactions and to produce symbol equations explain the evidence that a chemical reaction has taken place in terms of energy transfer and rearrangements of bonds between atoms use a particle model to predict the outcome of chemical reactions and to produce balanced symbol equations explain the evidence that a chemical reaction has taken place in terms of rearrangements of bonds between atoms, using the model of the differences of electron structure between elements use a particle model to predict the outcome of complex chemical reactions and to produce balanced symbol equations and ionic half-equations when appropriate explain the evidence that a chemical reaction has taken place (in a system at equilibrium) in terms of energy transfer and rearrangements of bonds between atoms Chemical and material behaviour 3.3 Patterns in chemical reactions describe, record and group observations from chemical reactions describe patterns in a range of chemical reactions link experimental and numerical data to illustrate a range of patterns in chemical reactions explain properties and patterns in reactivity in terms of particle model for atomic structure apply knowledge of patterns of reactivity in the periodic table to predict the outcomes of reactions from a range of familiar contexts apply knowledge of patterns of reactivity in the periodic table to evaluate critically a range of domestic and industrial processes including systems at equilibrium Crown copyright PDF-EN-13

4 4 The National Strategies Secondary You should be able to identify: how the principles from the Scientific thinking: developing explanations using ideas and models substrand translates into learning about particles and chemical behaviour how pupils are taught a simple model in, with only one kind of particle that pupils use a more refined model with more than one kind of particle in to explain elements, mixtures and compounds by pupils are expected to use a more refined model which includes the structure of atoms several examples of where a model that has been used in previous teaching has to be changed or made more sophisticated because the simpler model can no longer explain events. In other words it is no longer a good enough model at some point, of course, the simple model becomes not good enough and a more sophisticated model is needed. Task 1: School-based assignment This task will be more effective if you are working with a colleague or colleagues from your own department, but it can be carried out individually. Using particle models to explain phenomena Matter made of particles that are moving, very small and broadly of similar size. Matter made of particles that are moving, very small and can be different sizes and mass. When particles interact in a chemical change they swap places in a limited set of ways. changes of state: melting evaporating solidifying condensing diffusion expansion When particles interact there are forces acting between them. density osmosis Brownian motion Particles are of different types. There is a set number of kinds of atoms and all other particles are made from these. patterns of chemical change mass is conserved in reactions dissolving crystal formation elements, compounds and chemical change PDF-EN-13 Crown copyright 2009

5 The National Strategies Secondary 5 This is an example of an analysis of where the particle model is used in one science department s scheme of learning (scheme of work) for Key Stage 3. You will see that two main particle model ideas are listed for, two for and one for, together with the phenomena these are used to explain. Compare this with your department s scheme of learning for Key Stage 3. Which of these main particle model ideas are taught explicitly in your scheme of learning? Add any other phenomena you think pupils could attempt to explain with the model they are taught in each year group. For example, you may demonstrate the collapsing can experiment which gives pupils a good opportunity to apply the model of moving particles causing air pressure. Exploring pupils misconceptions about particles Many pupils have misconceptions about particles which tend to inhibit their learning. Even at the start of misconceptions about material changes are likely to be present: there are many accepted ways of revealing pupils misconceptions. Among these are concept mapping and related cognitive mapping methods. For example, this is the response from a high-attaining pupil who had studied material changes in the first term of when asked to show what they knew about the changes to materials when a candle burns. What misconceptions can you see? Alternative frameworks or misconceptions are views held by pupils (and adults) that do not fully coincide with scientific views. They can be held by a large proportion of the population or just by an individual based on personal experience and often they are developed through everyday talk. Crown copyright PDF-EN-13

6 6 The National Strategies Secondary Misconceptions may be: linked to everyday use of language constructed from everyday experience and are usually adequate for everyday life personal or shared with others used to explain how the world works in simple terms similar to earlier scientific models (e.g. the earth is flat) inconsistent with science taught in schools resistant to change. Many ideas pupils hold about the world around them come from sensory experience. Pupils construct a framework from these events that is coherent and fits their experiences but which may be very different from the scientific view. The scientific explanation can then seem counter-intuitive; for example gases have mass. Task 2: Where might misconceptions come from? The root of many misconceptions is often language. What is your response to the questions below? A) Expressions such as throwing a glance at someone could be why some people think that light travels from the eye to the object. Or turn the light off to save electricity could be why some people think that a bulb uses up electricity. Can you think of any other expressions or old wives tales that could cause misconceptions? B) Scientific words that also have an everyday meaning. The word force in everyday usage could be why pupils think a force is being applied during any movement. Switching between scientific and everyday usage can be confusing unless it is clearly explained and reinforced. For example, physics teachers will talk about measuring weight in Newtons and mass in grams, but chemistry teachers will talk about weight in grams. Outside lessons, physics teachers will also talk about weight in grams! Can you think of other science words where the everyday meaning might cause a misconception? C) Other causes of misconceptions can be our own observations. For example we see heavy objects falling faster than lighter ones; we see parachutes go upwards when the cord is pulled; we feel cold going into our feet when we stand bare foot on the floor. This often means that the scientific explanation feels counter-intuitive. Can you think of everyday observations that might account for pupils thinking that gas is bad but air is good ; boiling points are not fixed, i.e. temperature continues to rise if a liquid is heated; all liquids contain water? D) Sometimes models or diagrams used in text books can lead to misconceptions. Look through textbooks to find pictures or representations of: solid, liquid and gas models change of state structure of the atom processes like dissolving, diffusion, osmosis and Brownian motion. Think about how these could lead to misconceptions if the weaknesses in them were not made explicit PDF-EN-13 Crown copyright 2009