Understanding Atomic Models in Chemistry: Why Do Models Change?

Abstract

Understanding the role of early Greek philosophers (e.g., Democritus) and J. Dalton in developing the atomic theory is controversial among historians and philosophers of science. Chalmers (The scientist’s atom and the philosopher’s stone: How science succeeded and philosophy failed to gain knowledge of atoms. Dordrecht: Springer; 2009) claims that Dalton’s theory had no testable content. On the contrary, Rocke (Email to author dated October 30, 2013, reproduced with permission; 2013) considers that Dalton’s atomism is a successful theory. A study designed to evaluate the presentation of Dalton’s atomic theory in general chemistry textbooks (published in the USA) revealed that most textbooks stated that the atomic vision of Democritus was based on hypothetical questions (thought experiments), whereas Dalton based his theory on reproducible experimental results. Another study designed to evaluate the presentation of the atomic models of J. J. Thomson, E. Rutherford, and N. Bohr in general chemistry textbooks (published in the USA) revealed that most textbooks lack a historical perspective (although historical models are being presented) and provide a simplistic view of scientific models and how these change with no reference to the difficulties and controversies involved. Exactly the same HPS-based criteria were also used to evaluate textbooks published in Turkey, Venezuela, and Korea (general physics). The similarities of the textbooks published in four countries with different cultures and languages suggest that these textbooks have an underlying common thread, namely, the dominant empiricist epistemology. Due to the difficulties faced by Bohr’s model, A. Sommerfeld postulated elliptical orbits that provided greater stability to the atoms, leading to the Bohr–Sommerfeld model. A study designed to evaluate the presentation of the Bohr–Sommerfeld model in general chemistry textbooks (published in Italy and the USA) revealed that very few presented this model satisfactorily. Once again, textbooks published in two different cultures and languages were found to be very similar. Despite its success, the Bohr–Sommerfeld model went no further than the alkali metals, which led scientists to look for other models. These difficulties were resolved by Pauli’s exclusion principle and the wave mechanical model of the atom. It is concluded that understanding of atomic structure is a never-ending quest that requires imagination, creativity, and innovative techniques in the laboratory.