The roles of models in understanding science

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The roles of models in understanding science
Click the links below to access the activities

• Activity 1
• Activity 2
• Activity 3
• Summary

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Compare the maps
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1
Map showing TST MTR system map Geographic map of
the MTR
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2
Map showing TST MTR system map Geographic map of
the MTR
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Map showing TST MTR system map Geographic map of
the MTR
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Map showing TST MTR system map Geographic map of
the MTR
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This is a model of the land and sea of Tsim Sha
Tsui, highlighting train station exits
MTR map is a model of the routes of the MTR
trains.
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What is a model?
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A model as a representation of a real object
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A model as a representation of a system
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A model as a representation of a process
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A model as a representation of events
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A model as a representation of an idea
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When people draw maps, do they copy everything
they see?
If not, what criteria guide their drawing?
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Figure 1
Figure 2
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Activity 2
Draw pictures to illustrate the arrangement of
water particles in solid, liquid and gas state.
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gas
liquid
solid
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What is used to represent each water particle in
the model?
Spheres are used to represent water particles
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Information conveyed and drawbacks
In order to understand the three states of matter
(e.g. ice, water, steam), we used to use spheres
to represent water particles.
In this model, the composition of the sphere is
not our concern.
The composition of the sphere is not important
and may confuse our understanding of the
arrangement of particles in different states.
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Does anyone not use spheres to represent water
molecule/particles? Why?
Why do we use spheres even though we know that
water molecules are not spherical?
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What do you value about the model that you
learned in junior forms?
In order to better serve its purpose, when people
develop a model, it is most common that they will

• highlight the more relevant areas selectively
• neglect some less important aspects

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Activity 3
Methane molecules
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1.
5.
4.
6.
2.
CH4
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• In a group of 3-4,
• Name the type of model we used to represent
  methane
• Describe the information that each model conveys
• Describe the drawbacks of each model

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1.
5.
4.
6.
2.
CH4
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Name of the model Information conveyed Drawbacks
Space filling The relative size of different atoms (it shows covalent radii). Particularly useful when considering steric hindrance in SN reaction. Atoms or molecules are not hard spheres.
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Name of the model Information conveyed Drawbacks
Ball-and-stick Good three-dimensional representation. Bond angles can be shown more clearly. Sometimes, the balls are of the same size. The bond length and bond order (single, double or triple bond) may not be represented accurately.
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Name of the model Information conveyed Drawbacks
Dot-and-cross diagram Number of outermost shell electrons involved in chemical bonding. Bond order. Bond angle and atomic size cannot be shown clearly. Inner shell electrons are not shown.
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Name of the model Information conveyed Drawbacks
3D diagram The spatial arrangement of atoms can be shown in 2D. (without the trouble of building space-filling or ball-and-stick models) Atomic sizes are not to scale
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Name of the model Information conveyed Drawbacks
Structural formula Bond order (single, double or triple bond). the structure of a molecule (i.e. which atoms are bonded to which). Bond angles and electronic arrangements cannot be shown clearly.
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Name of the model Information conveyed. Drawbacks
Chemical formula The numbers and types of atoms in a molecule. A very convenient shorthand to represent a molecule universally, particularly when the molecule is made of many types of atoms. It cannot show the actual arrangement of atoms in a molecule.
CH4
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Can we have a true picture of a methane molecule
when we put all the information from these models
together?
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(No Transcript)
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Conclusion
Chemists or scientists use multiple types of
representation or models to convey their ideas.
None of these can truly and completely represent
molecules.
Each type of model highlights a particular set of
information while neglecting other information.
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Conclusion
Therefore, it is very important to be aware of
the scope and limitation of each model.
A deeper understanding can result from viewing
multiple representations or types of models.
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Conclusion
It may not be appropriate to judge a model that
you learn in an early stage of study (e.g.
particles as spheres) to be wrong.
While these models suffer from their explanatory
power, they have the advantage of simplicity.
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Other examples of models in chemistry
The shell and orbital models of atoms
Redox reaction (in terms of oxygen/hydrogen
transfer, electron gain/loss oxidation number)
Arrhenius and Bronsted-Lewis models of acid/base
Prediction of the shift in equilibrium position
in terms of Le Chateliers principle and reaction
quotient.
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Other examples of models
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• What have you learnt about the use of models in
  science?

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• What are the roles of models in science?

A model can be regarded as a representation of an
idea, an event, a process or a system.
A model is created to test ideas. It will change
or be modified to inform or assist the
development of those ideas.
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What are the roles of models in science?
A model helps us to represent ideas within a
defined scope.
A model is NOT a direct copy of reality.
When scientists develop a model, it is most
common that they will highlight the more relevant
areas selectively while neglecting some less
important aspects.