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Towards a more methodical approach to teaching senior chemistry.

What is scientific process?

Before a model for chemistry can be explored, it is useful to reflect on the work of science philosophers and on the nature of science.

It is unclear who first started to examine the universe in a systematic way; a way that has become incorporated into what we know today as the scientific method. Some say it was Roger Bacon, the 13th century Franciscan friar. Others say it was Francis Bacon, the Elizabethan judge. The confusion is perhaps understandable, especially as both served time in jail and both are reported as having died of a chill while attempting to stuff a chicken with snow (Collier's Encyclopedia, 1991; Moore, 1972). Roger was imprisoned for practicing magic and Francis for taking bribes. Francis' defence was that he accepted money from defendants, but it hadn't swayed his judgement as he still found the defendants guilty. Both have been credited with the method knownas inductivism.

Inductivism

Perhaps the least sophisticated and earliest attempt to describe scientific method is inductivism. This is summarised below:

Facts acquired through observation [right arrow] Generalisations are drawn from observations (induction) [right arrow] Scientific laws and theories

Falsificationism

Faislficatlonism was first proposed by Popper (1963 & 1968) and can be summarised as:

Theory [right arrow] Hypothesis (testable by experiment) [right arrow] Try to disprove hypothesis by experiment [right arrow] Hypothesis not disproved (provides further evidence for theory) or hypothesis disproved (theory rejected, new theory needed)

In this approach, theories are tentative and can be disproved by evidence which proves the theory incorrect.

Kuhn's Paradigms

Kuhn (1962) suggested a more social approach to scientific method:

PRESCIENCE [right arrow] NORMAL SCIENCE [right arrow] CRISIS [right arrow] REVOLUTION [right arrow] NEW NORMAL SCIENCE [right arrow] NEW CRISIS and so on

Pre-science is a period in which no theory has dominance over any other. In fact, Kuhn uses the word 'paradigm' rather than theory. What Kuhn meant by the word paradigm is unclear, but it would appear that it includes more than theory, defining avenues of investigation and the like. Eventually, one paradigm comes to be accepted by the scientific community over others.

There then follows a period of routine problem-solving, in which the paradigm is refined and explored. Anomalies arise which strike at the very core of the paradigm to give a period of crisis. This is followed by a revolution in which the scientific community shifts paradigms and so the cycle continues.

Kuhn's ideas have much to commend them. A look back in history gives several examples of scientists who suggested new ideas which did not fit in with the times. Galileo and Darwin are two examples that spring readily to mind. Kuhn's approach also includes the notion that, in the period of revolution, it is not the scientists who switch paradigms. Rather, the new paradigm is taken up by younger members of the scientific community while followers of the old paradigm die off.

Anarchy or chaos?

Feyerabend (1975) suggested there is no one method of science but that scientists use whichever approach is most suitable to their investigation. This is described as the "anarchic approach". Others would seem to adhere to this idea. Cross, Naughton & Walker (1986, p26) assemble a picture of "highly sophisticated epistemological chaos".

Nature of science

The philosophical descriptions presented above are all attempts to understand the nature of science. While a working knowledge of these specific philosophies is not necessary for effective scientific teaching, or even effective science, an understanding of the nature of science is very important. Indeed Lederman (1992) states, "'adequate understanding of the nature of science' or an understanding of 'science as a way of knowing' continues to be convincingly advocated as a desired outcome of science instruction". A brief summary of the nature of science is, "... the characteristics of scientific knowledge that necessarily result from the conventional approaches (i.e. scientific inquiry) scientists use to develop knowledge",

Lederman and Lederman (2004). Put extremely simply, the nature of science is the natural tendency for humans to interrogate their surroundings, gather information and subsequently establish patterns within acquired information with the goal of establishing reasonable future expectations. As teachers of science, it is our responsibility to communicate an understanding of the nature of science: that science is an exploratory endeavour which is constantly evolving and inherently human. This responsibility is written into, explicitly or not, the majority of scientific curricula.

Scientific inquiry

Scientific inquiry has many models for the process. Bell, Blair, Crawford & Lederman (2003) have identified six aspects of doing inquiry (formulating questions, designing investigations, dealing with data, constructing explanations, testing explanations against current scientific knowledge, and communicating results). Scientific inquiry describes more the nuts and bolts of what scientists do on a day-to-day basis, focusing more on how the information is gathered, patterns identified, and conclusions reached.

Lederman (2004) comments that the nature of science and scientific inquiry, "... are frequently described as distinct by science educators, but in daily concerns of the science teacher the two are so intimately related it is probably impractical on distinguishing between them".

The scientific process in the teaching

One of the aims of a science education is to expose students to scientific literacy so that they are able, Lederman & Lederman, (2004), "... to use scientific knowledge to make informed personal and societal decisions...". The value of a teacher's understanding of the nature of science and scientific inquiry is seen as critical if a teacher is to educate effectively, Lederman & Lederman (2004) says, "It is not difficult to argue that a teacher who lacks adequate conceptions of the Nature of Science and scientific inquiry is likely to be an inadequate teacher."The following aspects of scientific knowledge are identified, Lederman & Lederman (2004), "... scientific knowledge is tentative (subject to change), empirically based, (based on or derived from observations of the natural world), subjective (theory laden and a function of individuals' prior experience/knowledge), necessarily involves human inference, imagination and creativity (involves the invention of explanations) and is socially and culturally embedded" There are clearly areas where the work of the science philosophers overlap with these ideas, scientific knowledge is tentative (falsificationism), empirically based (inductivism), subjective (falsificationism), and is socially and culturally embedded (Kuhn's paradigms).

Milne (2014) identifies the following characteristics of science: science is a specific way of asking questions, science is using our senses to observe the world naturally, science is finding patterns in observations, science is developing theories which help us understand why relationships can be observed, science is making predictions, science is constructed by humans, which leads to the scientific community.

How then can students be presented with a clear picture of the scientific enterprise that is easily comprehended? The Australian Curriculum for chemistry answers these questions by detailing three interrelated strands of science. As the Australian Curriculum (n.d.) is the foundation of a number of chemistry courses being taught around Australia (NSW (2016), SA (2016), Victoria (2015) and WA (2017)) it is worth examining these strands in further detail.

Science Inquiry Skills

Science inquiry involves identifying and posing questions; planning, conducting and reflecting on investigations; processing, analysing and interpreting data; and communicating findings. This strand is concerned with evaluating claims, investigating ideas, solving problems, reasoning, drawing valid conclusions, and developing evidence-based arguments.

Science as a Human Endeavour

The Science as a Human Endeavour strand highlights the development of science as a unique way of knowing and doing, and explores the use and influence of science in society.

Science Understanding

The Science Understanding content in each unit develops students' understanding of the key concepts, models and theories that underpin the subject, and of the strengths and limitations of different models and theories for explaining and predicting complex phenomena.

The three strands of the Chemistry ATAR (Australian Tertiary Admission Rank) course should be taught in an integrated way. The content descriptions for Science Inquiry Skills, Science as a Human Endeavour and Science Understanding have been written so that this integration is possible in each unit. Australian Curriculum (n.d.)

Based on this information from the Australian Curriculum, it is apparent that the three strands have clear links with the philosophies of science, nature of science and science inquiry. What is proposed is a clear model for chemistry which can be used by teachers to integrate the three strands of chemistry and can be easily understood by students.

An approach to teaching chemistry

History has given us periods which were named after the materials used: The Stone Age, The Bronze Age, The Iron Age. Are we presently in The Silicon Age or perhaps The Plastic Age? The plethora of uses for these materials answer why we wish to investigate them scientifically and incorporate the Science as a Human Endeavour strand of the Curriculum. These materials are useful because of their properties, which are the first facts and hard pieces of evidence that theories can be built upon, this addresses how we find evidence to make and support scientific theories and incorporates the Scientific Inquiry Skills strand of the curriculum. More sophisticated scientific methods allow us to observe the structure of materials further refining the information available to scientists. Finally, we can use our developed theories and make testable predictions of further material behaviour, hopefully leading to deeper scientific understanding of the material. Of course, theories and models are proposed by people which also overlaps with the Science as a Human Endeavour strand. Each of the key words are part of the proposed model for organising content and process in secondary chemistry.

The diagram below simply summarises this progression of scientific investigation.

We hope that presenting students with this model at the start of a course in chemistry may lead them to a better understanding of what chemistry is and where the three strands fit in. This model draws inspiration from the philosophies of science described above. Indeed, Inductivism can be superimposed onto two of the boxes in Figure 1, specifically Tacts acquired through observation' (Observations and Properties) and 'Scientific Laws and Theories' (Theory or Model). Similar matchings can be made for Falsificationism and Kuhn's Paradigms. It would need to be explicitly stated to the students, and for each section of work, which parts of the diagram the students were studying and how they are related.

Examples of the model in use

1. Acids and bases

Any senior course in chemistry would cover acids and bases. When introducing acids and bases, a starting point could be a discussion of the uses (Science as a Human Endeavour) of acids and bases in everyday life such as preserving food (benzoic acid), making carbonated drinks (carbonic acid), cleaning metals and brickwork (hydrochloric acid), producing fertilisers and explosives (nitric acid), making detergents (sulfuric acid), manufacturing soft drinks (tartaric acid), producing fertilisers (ammonia), manufacturing gastric medicine (aluminium hydroxide), making cement (calcium hydroxide), manufacturing soaps and cleaners (sodium hydroxide), and making antiperspirant armpit deodorant (magnesium hydroxide). This would lead to experimental work on the properties (Science Inquiry Skills) of acids and bases and then an introduction to the Lavoisier, Davy, Liebig, Arrhenius and Bransted-Lowry models (Science as a Human Endeavour and Science Understandings) of acids and bases.

Lavoisier thought that all acids contained oxygen ([H.sub.2]S[O.sub.4]). Davy disproved Lavoisier's hypothesis (HCI) and suggested that all acids contained hydrogen. Liebig suggested that acids contain one or more hydrogen atoms, which can be replaced by metal atoms to produce salts. The Arrhenius Theory proposed that acids are substances that produce hydrogen ions when dissolved and that bases are substances that produce hydroxide ions when dissolved.

The limits of each theory can be explored and to provide an example of the ways in which models and theories are contested and refined when a new model or theory has greater explanatory scope and can be more broadly applied to make predictions. For example, The Arrhenius Theory has the following limitations.

* Can only classify substances which are dissolved in water.

* Ammonia solution plus hydrochloric acid to produce ammonium chloride can be explained using Arrhenius Theory. Ammonia gas plus hydrogen chloride gas to produce ammonium chloride cannot.

* Does not explain why some compounds containing hydrogen such as HCI dissolve in water to give acidic solutions and why others such as CH4 do not.

* Theory can only classify bases if they contain hydroxide ions and cannot explain why some compounds that don't contain hydroxide ions, such as sodium carbonate, have base-like characteristics.

Students can then be introduced to the Bransted-Lowry Theory which overcomes these limitations.

2. Metallic bonding

Metallic bonding could be introduced by asking the students to brainstorm the metals and uses that they encounter on a daily basis. A little bit of thought by the students should be able to produce the following: copper (wiring), aluminium (pots, pans, window frames, garden furniture and many more), steel (car bodies, construction, kitchen utensils and many more), zinc (galvanised surfaces), chromium (chrome surfaces).

Students could investigate the physical properties of metals--conductivity of heat and electricity, malleability, physical appearance (shiny or dull). Properties that are less practical/safe to examine in the school laboratory can be provided for the students. They could relate the physical properties of some of the metals to their uses (for example, copper is used for electrical wiring as it is a good conductor of electricity). Finally, the students could be introduced to the theory of metallic bonding and asked to make predictions regarding whether a substance has metallic bonding based on its properties.

3. Intermolecular forces

Intermolecular bonding could be introduced through solvents found in the home and their uses in dissolving different substances. The students could be asked to brainstorm solvents which may be found in the home, garage or shed. Perhaps a list looking like this may result: water, kerosene, methylated spirits, white spirit, nail polish remover. The students could investigate the solvent properties of some of these liquids, choosing those liquids that are safe to be used in the school laboratory. Materials to be tested could include: salt, sugar, bicarbonate of soda, butter or margarine, Epsom salts and then the students could perform experiments by adding the various liquids to one another (Will olive oil dissolve in white spirit for example). After coming to some conclusions about which materials are soluble in which solvents, then the students can be introduced to the theory of intermolecular forces and the students could make predictions about solubility.

4. Structure of benzene

Sometimes only part of the model may be used as other parts may be beyond the scope of the syllabus. An example is benzene, which is a very useful chemical. It is used to make plastics, resins, synthetic fibres, rubber lubricants, dyes, detergents, drugs and pesticides. However, this may be beyond the scope of a senior chemistry course, as may be the properties of benzene. (Benzene is a carcinogen and so would be best avoided in the school laboratory.) However, the model is still useful in demonstrating the dynamic nature of models and theories, which is part of the Australian Curriculum (n.d.) for chemistry. The dynamic nature of models and theories in chemistry can also be illustrated when discussing the structure of benzene. Students could be introduced to the Kekule structure of benzene, which was the first time a ring structure for the molecule had been proposed. The empirical formula for benzene had been known for a long time but chemists could not work out a structure which matched its unsaturated nature.

The students should be able to draw four using the Kekule structure. There are two isomers possible when adjacent carbon atoms are attached to a bromine atom but only three isomers exist.

Resonance where the molecule oscillates between two equivalent structures overcomes this anomaly.

However, the resonance structure has various anomalies. The stability of the benzene ring and its tendency to take part in substitution reactions rather than addition reactions being one.

Another anomaly is the bond lengths measured between carbon atoms in benzene.

* C-C bond length in benzene (from X-ray diffraction) is 140 pm

* Single C-C bond length is 154 pm

* Double C=C bond length is 133 pm

Thermochemical evidence also provides a third anomaly.

If cyclohexene reacts with hydrogen to form cyclohexane, the change in enthalpy is -120 kJ mol" (1).

[C.sub.6][H.sub.10] + [H.sub.2] [right arrow] [C.sub.6][H.sub.12] [DELTA]H = -120 kJ [mol.sup.-1]

Therefore, it would be predicted that for the three double bonds in the Kekule structure, the change in enthalpy would be 3 x -120 = -360 kJ [mol.sup.-1].

[C.sub.6][H.sub.6] + 3[H.sub.2] [right arrow] [C.sub.6][H.sub.12] [DELTA]H = -360 kJ [mol.sup.-1](Predicted)

However, the actual change in enthalpy for this reaction is -208 kJ [mol.sup.-1]

[C.sub.6][H.sub.6] + 3[H.sub.2] [C.sub.6][H.sub.12] [DELTA]H = -208 kJ [mol.sup.-1] (Actual)

Students can then be introduced to the model of benzene where all the bonds between carbon atoms are equivalent with three delocalised electrons shared with all the carbon atoms in the ring. In this example, the evolutionary nature of theories can be illustrated as well as the way in which theories are rejected on the basis of evidence and new theories developed.

Theories, explanations and predictions

One of the aims of The Australian Curriculum (n.d.) states, "understanding of the theories and models used to describe, explain and make predictions about chemical systems, structures and properties". It is therefore quite clear for the Australian Curriculum that theories and models are used to explain and predict the properties of matter. Unfortunately, some chemistry textbooks and syllabi have the properties of materials depending on the theory or model, one example being, Smith, Davis, Disney, Hayes & Whan (2014, p 263), which says, "Hydrogen bonding is responsible for the unique properties of water." Such an understanding would be difficult for students when presented with language where the properties of matter are dependent upon the theories and models.

Clearly this is not the only diagram or the only way to improve understanding of the scientific progression from observed properties to testable theories. We hope that by providing a new, simple tool aimed at emphasising an appropriate relationship between the properties of materials and the theories we use to explain them to inspire a more informed understanding of the scientific method used in chemistry.

Conclusion

Just as science itself is a constantly evolving and changing activity, the understanding of what science actually is, is constantly evolving and changing. That students' conceptions of the nature of science can be improved by overt teaching of the processes has been established by Bell et al. (2003) and Lederman (1992). The proposed model can be used to help students understand the interconnectedness of the three strands of chemistry in particular, as well as the evolutionary nature of science.

Acknowledgements

The authors would like to acknowledge and thank the help provided by Ms Georgina Goddard, teacher/librarian at Chisholm Catholic College and Emeritus Professor Mark Hackling.

References

Australian Curriculum, (n.d.). Chemistry: Structure of Chemistry - The Australian Curriculum v8.1. Retrieved June 26, 2018, from https://www.australiancurriculum.edu.au/senior-secondary-curriculum /science/chemistry/structure-of-chemistry/

Bell, R., Blair, L, Crawford, B., & Lederman, N. (2003). Just do it? Impact of science apprenticeship program on high school students' understandings of the nature of science and scientific inquiry. Journal of Research in Science Teaching 40(5), 487-509.

Collier's Encyclopedia. (1991). Collier's Encyclopedia. New York: Macmillan Educational Company.

Cross, N., Naughton, J., & Walker, D. (1986). Design method and scientific method. In A. Cross & R. McCormick (Eds.), Technology in Schools, Milton Keynes: Open University Press.

Davis, A. Smith, D., Disney, A., Hayes, V, & Whan, R. (2014). Nelson Chemistry Units 1 & 2 for the Australian Curriculum. Melbourne: Nelson.

Feyerabend, P. (1975). Against method. London: New Left Books.

Kuhn, T. (1962). The structure of scientific revolutions. Chicago: University of Chicago Press.

Lederman, N. (1992). Students' and teachers' conceptions of the nature of science: A review of the research. Journal of Research in Science Teaching 29(4), 331-359

Lederman, N. G., & Lederman, J. S. (2004). The Nature of Science and Scientific Inquiry. In The Art of Teaching Science. G. Venville & V. Dawson (Eds.). NSW: Allen and Unwin.

Milne, C. (2014) What is Science? In The Art of Teaching Science. G. Venville & V. Dawson (Eds). NSW: Allen and Unwin.

Moore, P. (1972). Stories of science and invention. London: Oxford University Press.

NSW Board of Studies. (2016). Chemistry syllabus. Retrieved August 25, 2016, from http://www.boardofstudies.nsw.edu. a u/syl la bus_hsc/chem istry.htm I

Popper, K. (1963). Conjectures and refutations: The growth of scientific knowledge. London: Routledge and Keegan Paul.

Popper, K. (1968). The logic of scientific discovery. London: Hutchinson.

SA. South Australian Certificate in Education. (2016). Chemistry syllabus. Retrieved June 26, 2018, from https://www.sace.sa.edu.au/web/chemistry/

Victoria. Victorian Curriculum and Assessment Authority. (2015). Chemistry syllabus. Retrieved May 22, 2018, from http://www.vcaa.vic.edu.au/Documents/vce/chemistry/ChemistrySD-2016.pdf

WA. WA Schools Curriculum and Standards Authority. (2017). Chemistry syllabus. Retrieved June 28, 2018, from http://wace1516.scsa.wa.edu.au/syllabus-and-support-materials/science/chemistry

Keith Dale is a former head of science with experience of teaching in the UK, Victoria, NT and WA.

Stephen G. Dale is a postdoctoral research fellow in theoretical chemistry under Emeritus Professor Axel Becke at Dalhousie University.
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Author:Dale, Keith; Dale, Stephen G.
Publication:Teaching Science
Date:Sep 1, 2018
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