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The physical construction of the chemical atom: Is there a way back?

The physical construction of the chemical atom: Is there a way back?. Mercè Izquierdo, UAB merce.izquierdo@uab.cat Agustin Aduriz-Bravo, UBA.

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The physical construction of the chemical atom: Is there a way back?

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  1. The physical construction of the chemical atom: Is there a way back? Mercè Izquierdo, UAB merce.izquierdo@uab.cat Agustin Aduriz-Bravo, UBA

  2. Science needs didactics of science to survive Science without the history of science does not imagine the futureDidactics of science looks at the futureand needs a science with history

  3. Science teaching and HS Histories that help learning HS STS Science model Resources In order to identify epistemological obstacles in the classroom

  4. There have been many contexts of scientific activity...

  5. According to the audiences, to economy, to politics...

  6. We will deal now with teachers’ chemistry. Disagreeing? How do representations (formulas, tables) and experiments interact?

  7. We have studied university textbooks from the first four decades of the 20th century We have studied some of the books written by the creators of the physical atom (1900-1930) We have studies the heuristic function of the periodic table in the construction of the physical atom

  8. The construction of the chemical atom was very difficult: Dalton formulates his ideas with ‘maximum simplicity’ Berzelius expresses the mass relations between elements in terms of atoms One-, two- or four-volume formulas?

  9. Mendeleev presents a system of chemistry based on elements… and we arrive at the end of the century with a very developed chemistry, without a physical atom

  10. The birth of physical chemistry • Cannizzaro uses physical data to calculate atomic mass and to organise organic chemistry • Physical and chemical properties are related Mendeleev did it. • New instruments are constructed: spectroscopes, polarimeters… new amazing phenomena appear!

  11. Radiations Energy, electromagnetism Chemistry Particles A diversity of styles of doing science: pragmatism, in the UK, the ‘look and see method’ criticised by Duhem (France)

  12. Cambridge: Maxwell, J.J. Thomson (1856-1940) Manchester: E.Rutherford (1871-1937), Moseley (1887-1915) Vienna: Boltzmann (1844-1906) Paris: M. Curie(1867- 1934), J. Perrin (1870-1942) Munich: A. Sommerfeld (1868- 1951), Heisenberg (1901-1976) Zürich: E.Schrödinger (1887-1961) Copenhagen: N. Bohr (1885-1928)

  13. New questions… new evidences • What is ether? Is electricity matter or movement? A new science of electricity is emerging: electromagnetism, new ideas about energy • Atoms are considered ‘old’ (Mach, Duhem, Le Châtelier, Urbain)… but young people (Perrin, Langevin, Curie…) are enthusiastic about particles! • Perrin’s book, Les atomes,(1913) is a landmark.

  14. Idealism – positivism - conventionalismpragmatism… A physical atom starts to be developed Textbooks begin to change

  15. Chemists: new ideas about electricity ‘atoms of electricity’ (Helmholz), ions (Arrhenius)Physicists start to build the atomZeeman (1896) calculates e/m (1897)J.J. Thomson compares this relation with that in electrolysis: the hydrogen-atom mass has to be 1000 larger than the electron mass

  16. J.J. Thomson (1856-1940) Atom representations – scale models He proposes a positive shell with electrons inside, in concentrical spheres

  17. A lot of radiations • Mme. Curie identifies radioactive elements (1896-1903) • Rutherford, 1898- 1907, relates Helium with alfa particles • Mendeleev rejects these new ideas about (chemical) atoms • Is it that atoms have grown an “incurable suicidal mania”? (Henry E. Armstrong, chemist) • It is difficult to explain atoms’ stability, but it is needed… because it has to be also a chemical atom

  18. The periodic table, a ‘heuristic’ • H. Moseley (1887-1915), with Rutherford (Manchester), identifies an ‘atomic number’. What did it mean? • Thomson’s proposal (a mechanical model for the atom) is accepted both by chemists and physicists, because it tries to explain periodicity

  19. A new model… among others • Rutherford: nuclear atom (1911) • Bohr chooses to work with him due his interest in the Periodic Table • Bohr-Sommerfeld’s physical model represents chemical atom (anschaulich) • Textbooks start to speak about n, m, l (after the First World War, the 1920s), and evidences about physical atoms begin to become accepted

  20. The wars: Heisenberg, Schrodinger… and the chemists • Bohr, Heisenberg (1922): The language of quantum mechanics should be use as in poetry… elicit images in conscience and establish symbolic links. Could we some time understand the structure of atoms? • Is it necessary to substitute mechanical models with mathematical models? • De Broglie invents a nice theory about the electron (doctoral thesis, 1923), and Schrödinger develops it (1926) • Bohr looks for correspondences between classical and quantum mechanics… complementarity

  21. Confrontation • Indeterminacy/uncertainty in the object or in the way of knowing it? • Heisenberg considers ‘revolting’ the wave equation • Bohr & Heisenberg do not agree with Einstein during the rest of their lives. They consider that knowledge refers to a real uncertainty in the nature of things. • Chemists go on doing chemistry…

  22. 1903 J.J. Thomson’s ideas: internal polarities created by ‘force-tubes’ H H H H C C H H H H 1919 Langmuir, from Lewis’s ideas, establishes covalent and electrovalent bonding H H C C H H Valence, kinetics, bonds… Chemistry was giving criteria

  23. Pauling, Professor • General Chemistry (1947): new textbook, chemistry is reconstructed, there is finally a chemical and a physical atom • A new way of considering the Periodical Table, interpreting periodicity with electronic configurations

  24. Linus Pauling explaning C tetra-valence: Chemistry has an atom, students can understand chemistry

  25. What is ‘understanding’? • ‘Having rules well related to experimental data • Having a mathematical structure well related to data • Having a ‘microstructure’ (batygen explanation)… but it is necessary to know what is done and what the question is

  26. Today, our students talk about the electronic structure of atoms, Lewis structures of compunds… but what is the meaning of all this for them? What kind of evidences about atoms, in chemical phenomena?

  27. Now, we cannot study chemistry without the PT… but electronic configurations is what is usually studies! • With this, do we teach how to DO chemistry??

  28. Conclusions: Textbooks nowadays do not differentiate the physical and the chemical atoms… Teh physical atom is given priority… but this would not have existed without chemistry But if there is no more chemistry, we will lose for sure this amazing adventure on how the physical atom was constructed from a chemical atom

  29. From Mendeleev to Pauling (two great teachers) From a system of chemistry… to a system of electrons But current students cannot walk the way back

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