Understanding Ionisation Energy: Physical, Chemical and Alternative Conceptions

There are many topics in chemistry where student performance in formal assessments may be considered to largely depend upon the understanding and application of concepts that may be un-problematically labelled ‘chemical’: concepts such as ‘element’, ‘neutralisation’, ‘addition reaction’, etc. However, there are also a number of curriculum topics from within chemistry where students are required to be able to demonstrate and apply ideas which in themselves may be seen as ‘belonging’ more to physics than chemistry. One such topic is that of ionisation energy, where basic electrostatic principles must be understood and applied. This paper discusses responses to a diagnostic instrument on Ionisation Energy which highlight student difficulties appreciating conventional physical principles. The instrument comprised 30 true-false items and was administered to over 300 college level chemistry students in 17 institutions in the UK. Respondents commonly agreed with statements reflecting previously identified alternative conceptions relating to the ‘sharing’ of nuclear force, and to the unconditional stability of species with full shells. The implications of the findings for the teaching of chemistry are considered, with particular reference to the debate about the extent to which chemistry can or should be reduced to physics. Chem. Educ. Res. Pract.: 2003, 4, 149-169