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Analogies provide lecturers with a tool that uses examples from real life and everyday experiences to help students understand scientific concepts and phenomena that are often, neither observable, nor, easy to imagine, by comparing or illustrating them with something that is recognizable, or to a concept with which they are familiar. Metaphors and analogical demonstrations can be particularly useful tools, for teaching chemistry because this field of science requires the mastering of many abstract concepts and complex counterintuitive phenomena. Such concepts and phenomena include: resonance, intermediates and transition complexes in reaction mechanisms, chemical equilibria, collision theory, theories of chromatographic separations, variation of atomic sizes in the periodic table, functional groups, resonance structures, polarizability and ionization of atoms and molecules, differences in reactivity between alkyl and vinyl halides, SN1 and SN2 mechanisms, theories of buffer solutions, the concept of environmental stress, sensitivity-response time-selectivity-noise- limit of detection of sensors, the concept of capacity (electrical, thermal, environmental, spatial, etc.), and many, many more.. .
Analogies can be used to teach abstract concepts using concrete examples. Of course, analogies have their limitations and we must keep in mind that they may on occasion lead students to develop misconceptions. Only, when students understand the target concept and the significance and limitations of the analogy, will effective learning be likely to be achieved. For example, the periodic variation of atomic sizes, which involves dimensions on a submicroscopic scale, is difficult for many students to visualize. When we say that the radius of one atom is twice that of another, students usually forget that according to the formula (4/3) x π x r3 the ratio of their volumes will in fact be 8. This can however be easily visualized using two balls having this relationship in their radii.
The use of analogies in teaching is a straightforward, challenging and enjoyable activity, but the wise teacher must choose analogies appropriate to the current knowledge of the audience.
Three examples of analogies that have been successfully used in teaching chemistry over a number of years are given here below.
Analogy between the voltage of a capacitor and the stresses on an ecosystem
The relationship between the sensitivity, the noise and the limit of detection for a detector
Analogy of chromatography and a Race over Hurdles