In many areas of chemistry and wider science, scientific theories or models  have been developed as the simplest explanation, often at the sub–microscopic level in order to account for observations in the macroscopic world. The development and extension of theories of acids and bases provides an example of such scientific development – when an existing theory cannot explain an observation, the theory is extended or superseded.

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When introducing an extended or new scientific theory, how can some students react?

Teachers can be accuse of having 'told lies last year' and students can think that, 'we have to forget what we learned and learn something new'.

How can teachers avoid these accusations and such worries of students?

When introducing or extending the model or theory, we must choose the words very carefully. Explain carefully that what we learned last year is not 'wrong' and it needs extended to take account of further observations.

For a more thorough exploration about some of the processes involved in developing, using and assessing a model, see the online RSC module on Developing and using models.