Nikos Psarros, Marburg
Index
Molecules: The bricks of the world?
The semantic function of the words – Predicators, abstractors and theoretical concepts
Chemical molecules and chemical atoms
Again: Are molecules the bricks of the world?
«the smallest unit[s] into which a pure substance can be divided and still retain the composition and the chemical properties of the substance» (Encyclopedia Brittanica, Lemma Molecule).
Thus for the physicist molecules are corpuscles that carry fundamental properties such as mass, extension, impulse or kinetic energy, that determine the mass, dimensions, velocity and temperature of a macroscopic inanimate body, for the chemist the so called ‘atomic composition’ and the structure of the molecules are responsible for the substantial composition of a body and its chemical properties and finally their mode of organisation in an organism and their function therein lays down the ground for the phenomena a biochemist, a biologist and for some a psychologist is called to study.
Taking the clay bricks that are used for the construction of a building as a metaphor for molecules, we could set up an analogy between a building and a macroscopical body like an organism, by saying that as the number and the mass of the bricks confines the mass and the dimensions of the building, their material and form determines the rigidity of the walls and their resistance against weathering and their way of joining is responsible for its architecture and its functionality as a house, factory, theatre etc., so – in the same manner – the various properties of the molecules “cause” the above mentioned properties of macroscopical bodies.
But the analogy between those two fields of human activity stops here because although the sciences devoted to the study of the “physical”, “chemical”, “biochemical” and “biological” properties of the molecules are put in the frame of an all-embracing “science of matter” of which they are hierarchically ordered sub-disciplines and the molecules are given a universal status as “bricks of the world”, it is not possible to say that the handicrafts concerned with the construction of buildings form a closed field of action that uses clay bricks as an universal material for its purposes. Indeed a closer look at the “model”, the construction handicrafts, reveals that they are not at all conceptionally related to each other. Buildings of the same architecture and functionality can be constructed from various materials either in a “discrete” (e.g. using bricks of stones) or in a “continuous” way (using concrete or steel) or in a combination of them. Similarly the desired degrees of resistance against the influence of weather and time can be achieved by many ways. Obviously there are some practical limitations to this but in any case the assertion that clay bricks are the fundamental constituents of all buildings and thus the unifying entity of brickmaking, masonry and architecture would be regarded even from the layman as ignorant and false.
We turn now our attention to the natural sciences and ask about the reasons that justify the conviction of many scientists that the molecules are the bricks of the world in spite the fact that the studied phenomena and the applied methods are as dispart as the techniques and the particular ends of the handicrafts that may participate in the erection of a house. The justification problem of this view is sharpened even more by the fact that in large areas of physics and biology, e.g. in kinematics, electrodynamics, evolutionary theory or ecology, there is no mention and no need for molecules in order to explain the phenomena. So what is the distinguished property of the concept of the molecule that makes it so attractive to the contemporary natural scientists, so that molecules have not only become inevitable parts of the “normal science” of our days but also parts of our life world? Why should molecules be regarded as the bricks of this world anyhow?
We cannot answer this question by visiting a laboratory and asking the chemists to show us some molecules or some of their constituents the atoms. They would reply that those particles are so small that they are invisible not only to the naked eye but also remain invisible even if we try the most powerful microscopes. The reason for this, we are told, lies in the very nature of the molecules and of the light. Molecules and light interact in a special manner, so that their existence can be proven only indirectly with very sophisticated machines, complicated measurements and a good training in reproducing phenomena in the laboratory, with other words only with the methods, the skill and the knowledge of a chemist or a spectroscopist. Already at this point we understand that molecules are in a different sense inivisible than, for example, microscopic bodies like dust grains or amoebas, and that scientists handle the word ‘molecule’ in a different way than e.g. the word ‘x-ray diffractometer’ or the word ‘naphthalene’. Thus the only way to answer the question of the last paragraph, i.e. to understand why the concept of ‘molecule’ is so important for – if anyhow – for the contemporary natural science, is to analyse the language of the scientists and to examine the semantic function of the word ‘molecule’ in their statements and theories. But what is meant by ‘semantic function of words’?
The meaning of words like ‘measurement’ ‘condensed’ and ‘x-ray spectrometer’ for example is revealed to the freshman students of chemistry by example and counterexample. The teacher shows them which action is called ‘measurement’ or ‘to measure’, which apparatus is called ‘x-ray spectrometer’, which process is called ‘condensation’ or ‘to condense’ and controls the success of his effort by requesting them to perform the desired action, to name the apparatus or to describe the process. Those words that are used in order to distinguish and to describe actions, things, situations and processes have the semantic function of predicators (Lorenzen 1987: 25 ff.)
When learning the use of words like ‘structure’ and ‘naphthalene’, however, the situation is quite different. These words cannot be introduced interactively, by example and counterexample or by demonstration of an action and request to repeat it. They do not refer to things, actions, processes or situations but they refer to an equivalence relation that is established between objects of predication. We can build two houses with the same arrangement of rooms, roofs, windows, doors etc., but from different materials e.g. one from clay bricks and wood and one from concrete and steel. Both houses are, however, in respect to the arrangement of their functional parts equivalent, so that we can say that they stay in the equivalent relation of being isostructural. By introducing the word ‘structure’ we can then talk about this equivalence relation without taking notice of the differences between both buildings. Talking about the structure of the houses we “abstract” from their rest properties hence the word ‘structure’ has the semantic function of an abstractor. It can be shown that the word ‘naphthalene’ is also an abstractor by establishing an equivalence relation between homogenous bodies in respect to some of their properties as melting point, odour, colour, chemical reactivity and so forth, and talking about two bodies as consisting of naphthalene when they share these properties.
Predicators and abstractors are used not only in scientific languages but also in our daily language. This gives them the advantage of providing the fundament on which a scientific language is developed as the objects they describe become objects of scientific research. The abstractors that are used to lay down the conceptional fundament of a science must, however, fulfil the condition that they are operationally introduced, i.e. that the equivalence relation they describe can be established by performing actions (Janich 1985: 83 ff.). Only in this way we can avoid the infinite regress in founding a scientific language or other unhappy effects like the acceptance of the so called theory ladeness of scientific terms or the violation of the principle of the methodical order (Janich 1985: 136, Janich 1987).
We have so far revealed the semantic function of words like ‘x-ray spectrometer’ and ‘naphthalene’, i.e. of predicators and abstractors. In our statement, however, we have still this ominous word ‘molecule’ that resists stubbornly any attempt to become subsumed under one of the introduced semantic functions. Grammatically the word ‘molecule’ is used like a predicator. We add, combine, split or determine its properties. On the other hand the object called ‘molecule’ is “invisible” but as we saw not in the same manner as a transparent, a very small or a hidden body. Furthermore the objects called ‘molecules’ do not occur in the life world. They are not something that we can buy in the market. Molecules occur only in scientific theories. Therefore we will call such an entity a theoretical construct (Hartmann 1993). The words describing them have thus the semantic function of theoretical terms or theoretical concepts.
Some phenomena, however, cannot be explained just by establishing relationships between objects that are described with predicators and abstractors. A famous example for such a case – and by the way the cause for the introduction of the molecules in chemistry – is the law governing chemical reactions between gases. As early as 1808 Gay-Lussac found out that when to gases were brought into reaction their volumes, either as reactants or as products, always form ratios of small integer numbers. Chlorine and Hydrogen for example react to form Hydrogen Chloride in a volume ratio of 1:1:2, Oxygen and Hydrogen react to Water vapour in a volume ratio of 2:1:2 an so forth. Every gas reaction – a chemical phenomenon – is thus accompanied by a reproducible variation of the volume of the reactants – a physical phenomenon. On the other hand there are many reactions between substances in the solid and/or the liquid state for which this law cannot easily been checked experimentally because these substances cannot easily be transformed in the gaseous state.
In order to explain the Gay-Lussac’s law the theoretical construct molecule has been introduced in the chemical theory. The chemists assumed that the “matter” of a given chemical substance is not homogeneously distributed in the volume that this substance occupied but that it forms small corpuscles, the molecules. The result of a reaction can now be interpreted as if the molecules of the one reactant are combined with the molecules of the other. Thus one molecule of Chlorine is combined with one molecule of Hydrogen to form one molecule of Hydrogen Chloride. Because a reaction is a chemical operation under controlled conditions, it has to be performed according to the norm of the constancy of mass and the norm of the constant proportions, i.e. the sum of the masses of the products of the reactions must be equal to the sum of the masses of the reactants and the products must show constant composition. Hence equal volumes of two gases must contain equal numbers of molecules. This would mean that one volume Chlorine gas and one Volume Hydrogen gas should produce one volume of Hydrogen Chloride gas, what is not the case. So it was further assumed that the molecules of Chlorine and Hydrogen are split during the reaction into “molecule halves” that recombine to form the molecules of Hydrogen Chloride. In our modern chemical terminology these “molecule halves” are the theoretical constructs atoms.
Let us now recapitulate the function of the theoretical constructs atom and molecule in the explanation of gas reactions:
The theoretical constructs molecule and atom help us to integrate both phenomena in one theory providing thus a good explanation for gas reactions.
Since its formulation in 1811 by Avogadro the modern molecular hypothesis has been proven very successful in explaining and integrating chemical phenomena and also in enabling the prediction of yet unknown ones. It has therefore gained a firm place in the chemical theory. The clarification of the semantic status of ‘molecule’ and ‘atom’ as theoretical concepts of the chemical theory explains also why we did not take up their use in ancient, medieval and early modern philosophical theories like the doctrines of Democritus, Lucretius or Gassendi or the chemical theories of Newton and Dalton.
The corpuscular chemical theories developed by Newton and his contemporaries in the 18th century are very interesting both from a historical and a philosophical point of view. They have been formulated in order to give a theoretical explanation of chemical phenomena using theoretical constructs in the sense reconstructed here. However, the explanation at that time for the chemical affinities of the substances relied on Newton’s gravitational theory that could give an account for the attraction between the molecules but was not adequate for the explanation of the particular affinities between given substances. This fact in combination with the lack of a normative frame for the performance of chemical reactions and the definition of the term “chemical compound” resulted in the rejection of the “gravitational” chemical theories by the beginning of the 19th century.
The atomistic ideas of J. Dalton who is sometimes regarded as the “Father of the atomic theory” are also localised in the realm of natural philosophic speculation. In 1808 Dalton published his main chemical work „A new system of chemical philosophy“ that in contrast to his title deals mainly with – from the modern point of view – physico-chemical problems. In the 3rd chapter of this book we find a “quasi-operative” definition of the various kinds of chemical compounds:
«If
there are two bodies, A and B, which are disposed to combine, the following
is the order in which the combinations may take place, beginning with the
most simple:
Dalton introduces further some «general rules» that1 atom of A + 1 atom of B = 1 atom of C, binary.1 atom of A + 2 atoms of B = 1 atom of D, ternary.
2 atoms of A + 1 atom of B = 1 atom of E, ternary.
1 atom of A + 3 atoms of B = 1 atom of F, quaternary.
3 atoms of A + 1 atom of B = 1 atom of F, quaternary.
etc., etc.» (Dalton 1965: 163).
«may be adopted as guides in all our investigations respecting chemical synthesis.
1st. When only one combination of two bodies can be obtained, it must be presumed to be a binary one, unless some cause appear to the contrary.
2nd. When two combinations are observed, they must be presumed to be a binary and a ternary.
3rd. When three combinations are observed, we may expect one to be a binary, and the other two ternary.
4th. When four combinations are observed, we should expect one binary, two ternary, and one quaternary, etc.» (Dalton 1965: 167).
Dalton, however, does not give any reason for the validity of these rules, nor does he correlate them to any empirical chemical phenomenon, so that the «deductions» he draws from them about the qualitative composition and the molecular mass of chemical compounds like water, ammonia, nitric acid, or (in modern terminology) carbon dioxide appear arbitrary. The consequence of these failed efforts for a corpuscular explanation of chemical phenomena was that the introduction of these theoretical constructs in chemical theories was discredited for a long time. Even the above mentioned successful corpuscular explanation given by Avogadro for the chemical and physical phenomena accompanying the reactions between gases did not manage to overcome the reservation against the atomistic chemical theories in chemical circles, a reservation that persisted until the beginnings of our century. Among the most convinced representants of this anti-atomist or anti-corpuscular party have been the 1905 Nobel laureate Wilhelm Ostwald and the today lesser known Czech chemist Frantisek Wald who in contrast to Ostwald opposed the atomic theory until his death in 1930.
They interact like completely elastic spheres
The eigenvolumes can be neglected in comparison to the gas volume they occupy
The forces between them result only from their collisions, especially they are not subject to any attractive or repulsive forces
Their velocities are statistically distributed so that
their mean velocity in a direction is given by the so called Maxwell equation:
This initial set of theoretical properties has been
later amended by the “shape of the molecule” and the “electron states”
(not by its “structure”) in order to take into account some inconsistencies
between the theoretical predictions and the measured “macroscopic” thermodynamical
values of a chemical substance. As we see the concept of the physical molecule
res. of the physical atom is quite different than that of the chemical
molecule res. chemical atom. Physical molecules do not display chemical
properties, therefore they do not fit into the definition of the Encyclopedia
Brittanica. Chemical atoms on the other hand are not “elastic” or “rigid”,
and they are subject to a variety of inter- and intramolecular forces that
determine in a high degree the chemical properties of the chemical substances
that are supposed to be built up by them.
«did not really emerge as a full-fledged science in its own right, with powerful experimental methods and predictive insight into biological phenomena, until the last quarter century. Two major developments brought this about. One was the recognition of multienzyme systems as catalytic units in the major metabolic pathways and the development of a unifying hypothesis for the transfer of energy in living cells. The other, which has had a most pervasive and profound influence, was the recognition that heredity [...] has a rational molecular basis. [...] The molecules found in living organisms not only conform to all the familiar physical and chemical principles governing the behaviour of all molecules but, in addition, interact with each other in accordance with another set of principles that we shall refer to as the molecular logic of living state» (Lehninger 1975: 4-5).
The axioms of this molecular logic of living state are according to Lehninger (ibid.: 7):
All living organisms have a common ancestor
The identity of each species of organism is preserved by its possession of characteristic sets of nucleic acids and proteins
There is an underlying principle of molecular economy in living organisms