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

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


1
  • The physical construction of the chemical atom
    Is there a way back?

Mercè Izquierdo, UAB merce.izquierdo_at_uab.cat Agust
in 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 future and 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!
  • Perrins book, Les atomes,(1913) is a landmark.

14
Idealism positivism - conventionalismpragmatis
m 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 atom Zeeman
(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?
  • Thomsons 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-Sommerfelds 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. Thomsons ideas internal polarities
created by force-tubes
H
H
H
H
C C
H
H
H
H
1919 Langmuir, from Lewiss 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) Fr
om a system of chemistry to a system of
electrons But current students cannot walk the
way back
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