1. MODELS IN SCIENCE TEACHING & LEARNING
What are models ?
A model is a representation of an object, event or idea. This representation creates a vehicle through which the object, event or idea can be conceptualized and understood. Models are important in science teaching, as major tools for teaching and learning. Models are one of the main products of science – the progress of science is normally marked by the production of a series of models, each associated with a distinctive theory. Modeling is a major element in scientific methodology

2. DIFFERENT TYPES OF MODELS
Mental model – that each of us visualizes in our mind;
Expressed model – when we try to explain or present in another form our mental model;
Consensus model – an expressed model which has gained acceptance within the scientific community;
Historical model – a consensus model which has been superseded at the ‘cutting edge’ of science e.g. the ‘plum pudding’ model of an atom is an historical model superseded by ‘orbiting electrons’ model.
A teaching model is one specifically produced to teach a difficult consensus or historical model.
The last four models can be put forward in a number of different ways including as objects, symbolic or mathematical representations, diagrams, spoken explanations or a mixture of
these.

3. Discuss 2D and 3D Models in chemistry teaching

4. SIX CHARACTERISTICS OF GOOD MODELS
Structurally complete in the relationship of its elements - ie has all the essential elements of the target idea;
Coherent and appropriate in its level of detail;
Considerate in its form – appropriate vocabulary and form of presentation;
Concrete in its representation – the relationship of all parts of the model are obvious;
Provides clear conceptual explanation – the associated theory can be explained through the model;
Highlights the correct comparatives between the model and the target idea – the scope and limitations of the model are pointed out.
These ‘6Cs’ can be used to evaluate the effectiveness of a model in exploring the target idea.

5. REASONS FOR USING MODELS
To help pupils visualize a structure or process;
To help less able pupils to remember a concept or idea;
To simplify a difficult concept or idea;
Because the pupils failed to understand a concept or idea on an earlier occasion;
To help the pupils link an unfamiliar idea with a familiar one, particularly in an imaginative way;
To entertain or to provide a variety of approach;
Because the pupils were encountering a concept or idea for the first time. (Jarman, 1996)

6. ANALOGICAL MODELS
Analogies are valuable thinking tools in helping students to learn and understand an unknown phenomenon in terms of the well known ones. They help in mental processing of abstract concepts which most of the times are the reasons why students find science very difficult to understand. . In science, for example, analogical reasoning is a common place, a well respected way of thinking and modelling and often used as a device in communications Far back in 19th century, electrons were pictured as behaving like light and waves. Water waves are known and familiar experiences to chiildren who go near and throw objects into a river. This was used as one to one mapping to illustrate the behaviour of electrons which are abstract, unknown and quite difficult to comprehend using waves that sudents are familiar with

7. Categorizing Models/Chemical Equilibrium
Assessing the efficacy of analogical teaching involves thinking
about the mode of analogy representation, their classification, and
the conceptual demands different models place on learners.
The representational mode of chemistry model presentation can be
concrete (e.g., ball-and-stick molecules),
verbal (e.g., analogical stories like those reported in this study),
mathematical (e.g., graphs of reaction profiles),
visual (e.g., STM images and 2D Lewis diagrams), and
mixed mode (Boulter & Buckley, 2000; Gilbert, Boulter, &
Elmer, 2000). A hidden mode is the personal mental models that
are generated or modified by teacher and textbook models.
Mental models are dynamic cognitive interpretations of target
concepts and often are unstable, incomplete, or ‘‘mental
muddles’’ (Greca & Moreira, 2000)..

8. CLASSIFICATION OF TEXTBOOK ANALOGIES
Classification. Curtis and Reigeluth (1984) classified textbook analogies under three types, based on each analogy’s degree of elaboration. The most common is simple analogy where thewriter says something like ‘‘activation energy is like ahill,’’ and leaves the student to interpret how activation energy is like ahill. Type two, enriched analogy, includes the grounds for the likeness; for example, ‘‘assembling a car is like the mechanism of a chemical reaction, because both cases proceed step by step.’’ The difference lies in telling the students how the analog is like the target. Type three, extended analogy, comprises multiple simple and/or multiple enriched analogies that describe and explain the same target. The elaborated ‘‘super-rubber balls in a box’’ analogy is an extended analogy as are several of the equilibrium analogies reported in this study.

9. ANALOGUES HAVE TWO PARTS
Analogy is made up of two parts, the target analogue, which is the domain to be explained, and the base analogue, which is the domain that serves as a source of knowledge.
The analogue domain is the one that exists in the memorry, from which the analogy is drawn, and the target domain which contains the science concept to be learned, the instructional objective of the analogy.
From the example given earlier, water waves is the domain analogue while electron behavior is the target analogue. We use the domain to explain the target.

10. TEACHING WITH ANALOGIES
When using analogy,teachers regularly preface their explanation with colloqual expressions such as “It’s just like ....”, “It’s the same as .....”, “It’s no different than.....”, and “Think of it as ...”.
In textbooks too, authors use more formal expressions like “Similarly ...”, “Likewise ...”, “Along related line ...”, “In comparison to ...”, and “In contrast with ...”
When you hear phrases like these what is being used is analogy which sometimes can be called mental models. What the teachers and the authors are saying in these expresions is “Let me give you an analogy”.

11. EXAMPLES IN TEACHING ATOMIC STRUCTURE
Topics
Teachers’ analogy
Target concepts
Mapping
Atomic structure and Periodicity
Crumb/particle of chalk
Combination of crumbs
A boy and a girl
Union between a man
and a woman marrying
Solar system with the
sun at the center and
the planets revolving
Particulate nature of
matter
Molecule, atom + atom
Cation and anion
Electrovalency
Electrons revolving in
orbits around the
nucleus.
Chalk particles are
very large
compared to atoms
or molecules
Mapping could be
established after
further explanation
to reduce
misconception.
There are more
than one electron
in some

12. MORE EXAMPLES Topics Teachers’ Analogues Target Concepts Mapping
Kinetic theory of matter
Spraying insecticide/
air freshner in a
toilet/ Perfume on
the body
Pressing piston on
air in bicycle pump.
Pressing becomes
difficult due pressure
Diffusion of
gases/ Random
movement
Pressure/Volume
relationship
Analogue and target structures match.
Gas molecules are the target. Gas pressure is as a result of collision of molecules against the walls of container. Mapping can be established on further explanation.

13. Analogies used by four chemistry teachers across 43 lessons
ANALOGUE
TARGET
Reaction rates
Students hurdling hurdles of different
heights
The student dance
Coconut shy
Climbing through a Swiss mountain
pass
Pushing a car around a side road
Chipmunks storing food before winter
Rates of various reactions having
different activation energies
Increasing in molecular velocities
causing an increasing number of
collisions
Effect of increasing concentration on
the number of successful collisions
Effect of catalysts on reaction
Mechanism and rate
Ease of catalyzed reaction mechanism
Exothermic and endothermic reactions

14. Breaking apart a pen and its cap Water flowing in and out of a sink
ANALOG
TARGET
Chemical Equilibrium
Breaking apart a pen and its cap
Water flowing in and out of a
sink
Gravitational effects on a body
Elastic band returning to its
original size
People moving in and out of a
shop
Person walking up a down
Escalator
Energy required to break chemical bonds
Constant dynamic properties in a steady state open system
Tendency of a chemical system to revert to equilibrium
Rates of forward and reverse
reactions for equilibrium
Competing forward and reverse
rates of reaction

15. RECOMMENDATIONS FOR USE OF ANALOGY
Use models at the beginning of a topic or integrated fully into the teaching of key ideas.
Where analogies are used, check pupils’ understanding of the analogy itself before using it to explain the key idea.
Show similarities and differences of the model to the target idea – i.e. highlight the strengths and limitations of the model.
Give pupils practice in developing their own models and use them to explain ideas. Highlight the strengths and limitations of their models
Encourage pupils to explore the use of (their) models in explaining related ideas – does the model still hold?
When using concrete models (e.g. drawings/ 3D models of atoms, bonding etc), 3D models seem to lead to greater understanding and retention of key ideas compared to 2D.
Enjoy using models – they provide an interesting, visual and stimulating way of understanding chemical ideas! Models can really help and motivate low achieving pupils.

16. A scientific model is a set of ideas that describes a natural process.
MORE ABOUT MODELS
A scientific model is a set of ideas that describes a natural process.
In Biology, the meiotic model describes the process by
which alleles segregate and independently
assort during gamete formation. Given this model and
some background knowledge about certain
genes of interest, it is possible to predict the possible
allele combinations resulting from meiosis
in a given sex cell or class of sex cells. The processes
of meiosis and fertilization are frequently
represented using Punnett squares

17. Models can be used to explain and predict natural phenomena.
One can use the simple dominance model to explain and predict
Inheritance phenomena in given organisms. One could explain
why a true-breeding tall pea plant crossed with a true-breeding
short pea plant always produces tall progeny and also why these
tall progeny, when cross-bred with one another, produce tall and
short progeny in a 3:1 ratio. Using the simple dominance model,
an explanation for such phenomena would take the form of
Specifying genotype to phenotype mappings (the relationships
between alleles is already specified in the model as one of simple
dominance) and describing how parent organisms with a given
genotype might contribute particular alleles to their offspring, via
meiotic processes, leading to organisms with particular
genotypes (and the consequent phenotypes).

18. Models are consistently assessed on the basis of empirical and conceptual criteria.
Specifically, scientists assess whether a particular model can
explain all of the data at hand and predict the results of future
experiments (empirical assessment). They also evaluate how well
A model fits with other accepted models and knowledge
(conceptual assessment—see Figure 3 for a summary). For
example, since the meiotic model is at some level a component of
he simple dominance model, it is important that there be no
conceptual conflicts between them. Models that fail to satisfy
some or all of the assessment criteria are discarded or (more
commonly) revised until they are deemed acceptable. In practice,
models are continuously revised as they are used to probe new
phenomena and collect additional data.

19. Models are useful as guides to future research.
Once constructed, models influence and constrain the kinds of questions
scientists ask about the natural world and the types of evidence they seek in
support of particular arguments. They guide a researcher’s perception of what
is involved in the natural processes of the world. The belief of early geneticists
that genotypes controlled discrete phenotypes only led them to see organisms
as mere aggregates of discontinuous traits. Important research for these
scientists included identifying just which characteristics could be identified as
traits’ and how such traits 6were inherited. Later, when geneticists began to
recognize the complexity of inheritance phenomena, they revised their earlier
models in order to account for inheritance of continuous characteristics as well. Their revised models led to new conceptions of how inheritance worked and, subsequently, new research questions as well.