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
2Science 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
3Science teaching and HS
Histories that help learning
HS
STS
Science model
Resources
In order to identify epistemological obstacles in
the classroom
4There have been many contexts of scientific
activity...
5According to the audiences, to economy, to
politics...
6We will deal now with teachers
chemistry. Disagreeing? How do representations
(formulas, tables) and experiments interact?
7We 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
8The 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?
9Mendeleev 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
10The 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!
11Radiations
Energy, electromagnetism
Chemistry
Particles
A diversity of styles of doing science
pragmatism, in the UK, the look and see method
criticised by Duhem (France)
12Cambridge 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.
14Idealism positivism - conventionalismpragmatis
m A physical atom starts to be developed
Textbooks begin to change
15Chemists 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
16J.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
18The 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
19A 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
20The 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
21Confrontation
- 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
221903 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
23Pauling, 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
24Linus Pauling explaning C tetra-valence
Chemistry has an atom, students can understand
chemistry
25What 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??
28Conclusions 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
29From 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