The Periodical TableIts Story and its

significance

Commented by: Mercè Izquierdo, Universitat Autonoma de Barcelona, SpainRita Linares, Universidad del Valle,

Colombia

Scerri’s book is a valuable contribution for researchers in chemistry education

Historical studies, made from a philosophical perspective, are very useful to understand both the evolution of ideas that were produced during more

than a century and the amazing persistence of ‘something’essential in the periodic table

From the perspective of didactical research we can also make specific contributions which would shed light on those aspects of the book that we find more

appealing.

For example, the interactions between the ‘inscriptions’ (as the table is) and scientific contents, and the results that can be obtained in terms of new

meanings thanks to such interactions

The periodical table is still and irreplaceable didactical instrument to teach chemistry. But some

people want to show that current table is no longer the one of Mendelejev, less theoretical.

What I would like to propose is that there is ‘chemical theory’ in Mendelejev Periodical Table and, contrary to what it may seem, today table is just a set of ideas about the physical aspects of the atom that current

students do not understand

The key is that the concepts of element and atom within the tradition of the ‘substances’ (in which I believe we should situate ourselves when teaching chemistry) appear very confusing in the teaching

chemistry.

As a consequence, the magnitude quantity of substance and its unity, the mole, are also

misunderstood

There is not lead in Spirit of Saturn

Beguin (1627); Lemery (1693)

Saturn calx and vinegar….destillation with a recipient very well closed…..

Discussion:

‘It is not well done the name spirit of Saturn … it is made from vinegar…because lead remains in the recipient

‘To see what is invisible

• To give meanig

of many actions

Identifying interactions with air components

‘Veure el que és invisible’

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Looking from conservation of somethings

Recovering the original chemical theory should be a key task nowadays, overcoming the epistemological

barrier that, for Mendelejev, the evidences referring to an internal structure in the atom supposed.

After this, we can accept, as the chemist done along the process of recovering the table for the new

chemistry, that the chemical atom is more than the sum of its

parts

It is necessary to know the work done by a lot of scientist, as described in Scerri’s book.

This work had this objective: understanding the relations between a ‘whole’ (the chemical atom) and

its parts

Radiations

Particles

Energy, electromagnetism

Chemistry

Pragmatism,conventionalism…’Anschaulich’And two wars….

Cambridge: Maxwell,J.J.Thomson (1856-1940)

Manchester: E.Rutherford (1871-1937), Moseley (1887-1915)

Munich: A. Sommerfeld (1868- 1951),Heisenberg (1901-1976)

Zürich: E.Schrödinger (1887-1961)

Copenhagen: N. Bohr (1885-1928)

Viena: Boltzmann (1844-1906)

París: M. Curie(1867- 1934),J.Perrin (1870-1942)

Contrast between the constancy of the didactical value of the periodic table with the changes that it suffered

regarding the meaning of the periodic law is puzzling.

What function has didactics of chemistry in the process of building the physical atom from Mendelejev’s day to

present day?

What function has today the Periodical Table in teaching chemistry?

From a study done by Rita Linares (Colombia) about the uses of the Periodic table on three levels (books and

JCE, teachers and students) we have had evidence of the problems to which a deeper knowledge of the periodic

table might offer a solution.

I will only refer here an abstract: teachers and students

We asked 15 university teachers about the function of Periodical Table in chemistry teaching

We were able to classify teachers in three groups:*didactical function (to teach general chemistry)*organising function (to systematise information)

*‘macro’ function (knowing the elements in order to explain phenomena)

We considered that it was necessary to ask more explicitly on the concepts of element, atom and simple

substances:Could you please define what an element is for you? Are

elements, atoms and simple substances the same?

We identify 29 different relation, which we interpreted as five different ‘view’according the relevant aspect

that teachers highlight.The view were: substance, atom, symbol, species,

undefined

Correlation was establish quite clearly:

Didactical function …………elements as simple substance The Periodic Table is an instrumentthat

permits to teach principle of chemistry based on the modern quantic atom

Organising function…………element as a symbol or an atom The Periodic Table helps decrease the entropy of

knowledgeMacro’ function………undefined view . The periodic Table is an instrument to undersatnd, step by step, the

chemical chemistry

Questioning such a basic concept as that of ELEMENT has been an opportunuty for university teachers to reflect on their own teaching practice: on the language that they use, the consistency of their knowledge, the coherence of

their didactical transposition

And by students?

Confusion between element and simple substance: difficulties with the concept of mole and with Avogadro’s

number

Inexistence of the magnitude ‘amount of substance’

All this shows the centrality of ELEMENT concept and how important

is to understand very well how chemist has contributed to the construction of a physical atom that save the Table of

Chemical Elementsas a ‘System of Chemistry’

The process is very well described in Scerri’s book

In spite of the philosophical subleties derived from the different levels of ‘reality’ to which chemistry teachers refer, they all believe in the reality of the chemical atom though they explain, in the vast majority, as the physical

atom.

The differences between these two atoms (the daltonian or chemical atom, the quantic or physical atom) could very good established after reading Scerri’s book, but more

discussion is needed

Scerri’s contributions are useful for teachers in terms of:*becoming aware of the complicities between the periodic table and the evolution of new ideas about the structure of

the atom* Showing how the cause of periodicity was found in the

structure of the atom*Analysing the consequences of this shift in the meaning

of the periodic table

It will be possible:*Articulate chemistry teaching proposals from current periodic table(s) taking into account that it will have to contribute to rationalising real chemical facts from the

concepts of element, mole and ability to react* Differentiate the ontological and explanatory status of

chemical elements.*Reflect around the table format, because of their evident

didactical intentionality

Some questions are rising:*Can be suspect that there are two ‘atoms’: Mendelejev’s

atom and quantic atom?Should be the Periodic Table a data base, a law suggesting

a particular arranging of the electrons, a law suggesting chemical interactions?

*Could be use different tables, as we has seen in this historical review?

How is the chemistry of our new Periodical

Table?

One…or two?

Not this chemistry

Nor this

Iron + Oxigen

Iron oxide

This?

Linus Pauling and the quantic explanation of the cub of Lewis

Or this?

Could be state that teaching was (is) a vector of the development of scientific knowledge?

As teachers, are we also contributing to develop scientific knowledge?

I Think so!