The Changing Relation Between Atomicity and

The Changing Relation Between Atomicity and Elementarity: From Lavoisier to Dalton Marina Paola Banchetti-Robino Florida Atlantic University

Introduction The concepts of ‘atomicity’ and of ‘elementarity’ have a long and venerable history both in philosophy and in chemistry. Although ‘atomicity’ and ‘elementarity’ served to elucidate the fundamental nature of material substances both for natural philosophers and for chemists, these notions were never interchangeable since they were grounded in different conceptions of fundamentality.

‘Fundamentality’

Metaphysical Sense

Ontological Sense

2 For our purposes, fundamentality can be understood either in a more general metaphysical sense concerned with the ultimate nature of reality or in a narrower ontological sense concerned with existent entities and how these can be hierarchically organized. For these reasons, these two meanings of fundamentality are not necessarily co-extensive

‘Atomicity’

‘Elementarity’

‘Fundamentality’

Metaphysical Sense

Ontological Sense

Given the way in which atomicity and elementarity were conceived throughout the history of speculative and natural philosophy, we see that elementarity has been traditionally associated with fundamentality in the ontological sense, while atomicity has been associated with fundamentality in the metaphysical sense.

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Elements • “Elementum” – Principle (ontological notion) • Elements are not mereologically metaphysically fundamental • Empirically observable determinable properties

substances

irreducible with

or

empirically

• Properties of individual material bodies are ontologically dependent on the properties of the elements that compose them

From the classical to the early modern period, elements were generally regarded as the principles upon which the properties of existing things depended. Elements were not considered mereologically irreducible or metaphysically fundamental. They were regarded as being observable substances with empirically determinable properties. The complex properties of material bodies were considered ontologically dependent on the simple properties of the elements that compose them.

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Four Aristotelian Elements • • • •

Air – Cold Fire – Heat Earth – Dry Water - Moist

Paracelsian Tria Prima • Sulfur – Flammability / Combustibility • Mercury – Volatility / Stability • Salt - Solidity

One obvious example are the four Aristotelian elements. Aristotle did not consider the four elements to be metaphysically fundamental.

Amorphous matter was metaphysically

fundamental, and the four elements represented the ways in which matter is organized in the world of existing things. Even those alchemists who rejected the four Aristotelian elements accepted the view that the properties of material bodies depended upon those of constituent elements or principles. For Paracelsus, for example, these elements or principles were tria prima, that is, the three metallic principles of sulfur which corresponded to flammability or combustion, mercury which corresponded to volatility and stability, and salt which corresponded to solidity.

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Atoms • “Atomos” – Absolutely (metaphysical notion )

indivisible

and

monadic

• Mereological irreducible (indivisible) • Properties of shape, size, and motion • Unobservable in principle – Properties not empirically determinable • Metaphysically ultimate substances

On the other hand, for both classical and early modern atomists, atomism was a metaphysical thesis purporting to establish claims about the ultimate nature of matter. They regarded atoms as all having the same properties of shape, size, and motion and as being indivisible, that is, mereologically irreducible.

Since such entities were considered

unobservable in principle and their properties were not empirically determinable, the belief in their existence was founded more on metaphysical speculation than on sound empirical evidence. Rather than being an empirical notion, the notion of ‘atom’ was the idea of ultimate substances that grounded all material being.

6 Since atomos were understood as being indivisible, one of the debates that ensued as a result of the early modern revival of atomism was whether any physical particle could ever truly qualify as an ‘atom’.

René Descartes (at one extreme) • The essence of matter is extension • All material bodies, no matter how small, are divisible • No physical particle can be atomic • The only true atom is the mathematical point (dimensionless) Giordano Bruno (at other extreme) • Three-fold minimality

understanding

of

‘atomicity’

or

mereological

• Mathematical minimo: Point • Physical minimo: Atom • Metaphysical minimo: Monad

Many natural philosophers fell somewhere between these two extremes and several chose to postulate corpuscles, rather than atoms, in order to dispense with the notion of indivisibility.

This debate over atomicity reflects the intimate relationship between

metaphysics and natural philosophy that persisted in the 16th, 17th and early 18th centuries. Chemists working during the second half of the 18th century, however, considered atomistic theories to be primarily speculative attempts at conceptualizing the fundamental grounding

7 of nature. Although many of these chemists payed lip service to Newtonian atomism for example, it became increasingly clear that atomism offered little of heuristic or practical utility to chemist1 and that they could easily dispense with speculative theories regarding fundamental particles. For example, Etienne Geoffroy’s tables of affinity, which in no way depended upon any speculations about the ultimate nature of matter, “summarized experimental data acquired by manipulating substances in the laboratory and became efficient devices for ordering chemical experience and guiding research.”2 As Ursula Klein has argued, Geoffroy’s work “shows how a large section of [18th century] experimental chemistry could be construed as a practical tradition divorced from a speculative metaphysics, atomistic or otherwise.”3

Antoine Lavoisier (1743-1794)

Antoine Lavoisier (1743-1794)

It is against this background of chemical practices and attitudes that Antoine Lavoisier’s own perspective regarding the nature of fundamental atoms should be contextualized. For Lavoisier, atomicity is a suspect metaphysical notion and he rejects the epistemic and

8 heuristic value of positing indivisible atoms as the grounding of all material reality. In the preface of the Traité Élémentaire de Chimie (1789), he makes a clear break with early modern chymistry’s still intimate relation with speculative metaphysics and explains the general principle that he proposes to apply to his chemical studies. He states,

“When we first begin to undertake the study of a science, our relation to that science is analogous to that of children … Just as in a child, it is ideas that are the product of sensation, it is sensation that gives birth to an idea, so it is for that individual who begins to undertake the study of the physical sciences: Ideas must only arise as a consequence, as an immediate result of, an experience or sensation. ” Antoine Lavoisier, Traité Élémentaire de Chimie (1789)

For Lavoisier, just as correct ideas can only arise from experience, a priori notions that are contrived by the imagination or by the faculty of reason unchecked can lead us into serious epistemic and scientific error. He claims that,

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“The only way to avoid such errors is to suppress or at least to simplify as much as possible our reasoning … which alone can lead us astray … Convinced of these truths, I have imposed upon myself the rule of proceeding only from the known to the unknown, and of deducing no consequence that does not immediately derive from experience and observation. ” Antoine Lavoisier, Traité Élémentaire de Chimie (1789)

In spite of the sympathies that he may have had for the kind of Newtonian atomism championed by Laplace, Lavoisier regards chemistry as an empirical practice and he makes every effort to distance his new science from any form of atomism. In order to avoid what he considers to be the errors of his more speculatively inclined early modern predecessors, Lavoisier turns the focus of chemical theory and practice towards ‘elementarity’ and towards the experimental isolation and quantitative description of ‘chemical elements’. He thus proposes a reformed nomenclature for chemistry in which the names of compound substances reflect their elementary composition 4 , thus avoiding any reference to atoms, corpuscles, or the minutest particles of matter. To clarify what he means by ‘element’, he explains that

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“If by the name of element, we mean simple and indivisible molecules that compose bodies, it is probable that we do not know them: if, on the contrary, we attach the name of element or principle of bodies to the idea of the last point at which analysis arrives, all of the substances that we have not yet been able to decompose by any means are, for us, to be considered elements.” Antoine Lavoisier, Traité Élémentaire de Chimie (1789)

As Robin Hendry points out, this analytical, pragmatic, and operational definition provides a criterion for deciding when a substance should be regarded as an element, but it does not tell us what the term ‘element’ means.5 Lavoisier’s system is the culmination of the experimental program involving the investigation of the analysis and synthesis of chemical substances, and he also considers that chemical analysis goes hand in hand with weighing, which provides a way of regulating, shaping, and validating chemical experiments and theories. Together, these two techniques provide a way to replace the old ideas about elements with the new concept of simple substances with determinable and measurable volumes that can be converted into their corresponding weights. By 1789, Lavoisier uses

11 analysis and weighing methods to produce a list of chemical elements, which he then subdivides into four general categories on the basis of their chemical properties.

Lavoisier understands that the limits of analysis of his time are probably only temporary and that future analytical methods might succeed in further decomposing what he calls chemical elements. He, thus, admits that the table of elements derived by this operational approach is provisional and entirely open to revision. He states,

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“We cannot assure that the substances that we regard as simple are not themselves composed of two or perhaps a greater number of principles. However, since these principles cannot be separated or, rather, since we have no means of separating them, they behave for us in the manner of simple substances, and we must not assume them to be composed until experience and observation prove otherwise. ” Antoine Lavoisier, Traité Élémentaire de Chimie (1789)

Thus, although the properties of compound substances are considered ontologically dependent on the properties of the chemical elements that compose them, this dependence is epistemically provisional until these elements can be further analyzed into simpler substances to reveal a deeper level of ontological dependence. Because Lavoisier’s system of chemistry precludes connecting chemical elements with fundamental particles, the formerly intimate relation that had existed between metaphysics and early modern chymistry is severed. After this point, no atomic theory could garner scientific credibility unless it could somehow disentangle ‘atomicity’ from its association with metaphysics and render it into an empirical and quantitative notion. This disentanglement and transformation of the concept of ‘atomicity’ would finally occur as a result of the development of chemical atomism by 19th century chemist, John Dalton.

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John Dalton (1766-1884)

John Dalton (1766-1884)

Dalton’s New System of Chemical Philosophy (1808) affirms his commitment to Lavoisier’s operational and analytical definition of elementarity, which had become conventional for chemists by the time we reach the 19th century.6 In a manner similar to Lavoisier, Dalton states that

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“By elementary principles, or simple bodies, we mean such as have not been decomposed, but are found to enter into combination with other bodies. We do not know that any one of the bodies denominated elementary, is absolutely indecomposable; but it ought to be called simple, till it can be analyzed. ” John Dalton, New System of Chemical Philosophy (1808)

However, while conducting meteorological studies in which he examines the properties and behavior of gases, Dalton asks a number of important questions that will lead to inquiring about the compositional nature not only of gases but of all elementary substances. He asks,

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• Why do different gases have different solubilities in water? • Why are light and elementary gases such as hydrogen and oxygen least soluble, while compound gases such as carbon dioxide are very soluble? • Is solubility proportional to density and complexity?

These questions fuel Dalton’s desire to ascertain the compositional nature of gases and of elementary substances but to do so in a way that meets Lavoisier’s strict empirical and quantitative requirements. Dalton ultimately decides on the assumption, which he believes is supported by observations, that gases and chemical elements are composed of ‘ultimate particles’ or atoms.

7

Dalton conceptualizes atoms as dense spherical particles, each

surrounded by a subtle fluid or ‘caloric’, which prevents these particles from being drawn into actual contact with one another. He claims that this is proven by the observation that the bulk of a body may be diminished by abstracting some of its heat.8 He regards chemical reactions as the shuffling and reshuffling of atoms into new clusters and, influenced by Newton’s idea of forces of attraction, he writes:

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“Observations have tacitly led me to the conclusion which seems universally adopted, that all bodies of sensible magnitude, whether liquid or solid, are constituted of a vast number of extremely small particles, or atoms of matter bound together by a force of attraction, which is more or less powerful according to circumstances, and which … endeavours to prevent their separation, and is very properly called … affinity … Besides the force of attraction … we find another force that is likewise universal, or acts upon all matter which comes under our cognizance, namely, a force of repulsion. ” John Dalton, New System of Chemical Philosophy (1808)

Although this may seem like a return to the speculative atomism that had been supplanted by Lavoisier, Dalton buttresses his chemical atomism by postulating that there are as many distinct atoms as there are distinct chemical elements. He assumes that atoms of the same element are similar in shape and mass but differ from atoms of other elements. He postulates that the properties of a compound substance are determined by the properties of its constituent elements and that the properties of each element are determined by the properties of the distinctive atoms of which it is composed. He thus reconceptualizes the notions of

17 ‘atom’ and of ‘element’ by subsuming both under the concept of fundamentality understood as ontological dependence. Dalton regards the antagonism between the forces of attraction and repulsion affecting atoms, as well as the quantities of heat surrounding each atom, as accounting for the differences between gaseous, liquid, and solid bodies.9 He states,

“Gases consist of corpuscles that repel each other when exposed to heat … It is necessary to differentiate the corpuscles or atoms of the gases not only by size or by shape but also by weight.” John Dalton, New System of Chemical Philosophy (1808)

18 Regarding the solubility of gases, he concludes that

“The circumstance depends upon the weight and number of the ultimate particles of the several gases: those whose particles are lightest and single being least absorbable, and other more according to their increase in weight and complexity. ” John Dalton, New System of Chemical Philosophy (1808)

One can see how this line of reasoning would then lead to an inquiry into the relative weights of chemical atoms. 10 In seeking to conduct such an inquiry, Dalton eliminates the intangibleness implied by metaphysical atomism and has fixed a determinable property to chemical atoms. Dalton believes that the relative weights of atoms can be determined by measuring the relative weights of elements that are isolated during the analysis of compounds. Thus, availing himself of the highly precise data provided by Lavoisier’s research,11 Dalton proposes to use analysis to isolate the component elements of compound substances and to measure their relative weights. He explicitly states that,

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“It is one great object of this work, to shew the importance and advantage of ascertaining the relative weights of the ultimate particles, both of simple and compound bodies, the number of simple elementary particles which constitute one compound particle, and the number of less compound particles which enter into the formation of one or more compound particles. ” John Dalton, New System of Chemical Philosophy (1808)

In order to move from the measurement of the relative weights of elements to the relative weights of their constituent atoms, Dalton must make a number of assumptions both about chemical reactions and about chemical composition. One of these assumptions is the Law of Conservation of Mass. Agreeing with Lavoisier, Dalton concludes that atoms can neither be created or destroyed in chemical reactions. He states,

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“Chemical analysis and synthesis go no farther than to the separation of particles one from another, and to their reunion. No new creation or destruction of matter is within reach of chemistry. ” John Dalton, New System of Chemical Philosophy (1808)

He also assumes the Rule of Greatest Simplicity, so that chemical formulae are always to take the simplest form that is compatible with the empirical data. Therefore, Dalton postulates that,

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“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 [combination]: namely, binary [AB], ternary [A2B or AB2], quaternary [A3B or AB3], &c. ” John Dalton, New System of Chemical Philosophy (1808)

Dalton’s theory also places Joseph Proust’s Law of Definite Proportions on firm theoretical ground by assuming that compounds are made of combinations of different types of atoms in fixed proportions, regardless of the source or method of preparation. Regarding the composition of compound substances, Dalton formulates the Law of Multiple Proportions stating that

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“When two elements combine to form two or more compounds, the ratios of the masses of one element that combine with the fixed mass of the other are simple whole numbers ” John Dalton, New System of Chemical Philosophy (1808)

Armed with these postulates and with empirical data provided by chemical analysis and measurements using the precision balance, Dalton proceeds to calculate the relative weights of chemical atoms from experimental data about compound substances, using hydrogen as the fixed unit so that “the atomic weight of each element [is] the gravimetric proportion that combine[s] with a gram of hydrogen to form the most stable combination.” 12 So, for example,

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After having collected enough data on relative weights, Dalton moves on to create his famous tables of elements, which grow larger and more complex over the course of 24 years as he is able to identify more and more elements based on relative weights and atomic masses.

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Table of Elements (1803)

20 in 1803

Table of Elements – New System of Chemical Philosophy (1808)

20 in 1808, accompanied by their various binary, ternary, quaternary, etc. combinations

25

Table of Elements – New System of Chemical Philosophy, Second Volume (1827)

36 in 1827

Dalton’s chemical atomic theory and some of its assumptions certainly generated some controversy among 19th century chemists, and many of Dalton’s contemporaries continued to sympathize with Lavoisier’s view that all atomic theories were ultimately bound to be metaphysical.13 For these reasons, several 19th century chemists chose to use atomic theory as a convenient instrumental device, without making any ontological commitments to the reality of atoms. Other chemists, on the other hand, rejected atomism altogether. For example, the great physical chemist Wilhelm Oswald held out against atoms into the 20th century, believing that the facts of chemistry could be better accounted for thermodynamically.14

26 We also know that Dalton’s rigid and arbitrary assumptions led to some erroneous conclusions about composition and weights. Later chemical discoveries showed that there are violations of Dalton’s postulates.

Violations of Dalton’s Postulates: • Violation of Law of Definite Proportions: Ø Example: Ferrous oxide - Actual formula is non-stoichiometric (Fe0.95O, thus Fe1-xO), rather than the more ‘ideal’ stoichiometric formula (FeO). • Violation of Law of Multiple Proportions: Ø Example: Sucrose (C12H22O11) and other complex organic compounds.

For instance, ferrous oxide whose actual formula is non-stoichiometric (Fe0.95O so Fe1-xO), rather than the more ‘ideal’ stoichiometric formula (FeO) violates the Law of Definite which requires a ratio of whole integers. Complex organic compounds like sucrose, whose formula is C12H22O11, violate his Law of Multiple Proportions. As well, although Dalton dissociates atomism from metaphysics, he conceptualizes the ontological dependence of properties on atomic mass and composition in a way that is too simplistic. Being unaware of the

27 dependence of chemical properties on the structural arrangements of atoms, chirality, and other factors, Dalton was unable to predict and would have been unable to explain many types of chemical compounds later discovered. For instance,

Dalton’s atomic theory is unable to predict or explain: Isomers of different types Enantiomers, Diastereomers):

(Constitutional

Isomers,

Stereoisomers,

Ø Example: Butane (C4H10) – melts at -138.4o C and boils at -0.4o C Isobutane (C4H10) – melts at -159.42o C and boils at -11.7o C • Isotopes: Ø Example: Chlorine 35 and chlorine 37 – Same element, different masses and densities. • Isobars: Ø

Example: Argon atoms and calcium atoms - Different elements, same atomic mass (40 amu).

• Allotropes: Ø Example: Charcoal, graphite, and diamond as allotropes of carbon – Same element, different properties

28 In spite of its errors, however, Dalton’s atomic theory did present a number of new and important concepts.

Contributions of Dalton’s atomic theory: • Rendered intelligible the hundreds of quantitative analyses of substances recorded in the chemical literature • Provided a model for the long-standing assumption that compounds were formed from the combination of constant amounts of their constituents • Explained discontinuity in the proportions of elements in compounds (laws of definite and multiple proportions) • Suggested that arrangement of atoms in a compound could be represented schematically in a way that indicated the actual structure of the compound • First major attempt at reconciling empirical and quantitative requirements of modern chemistry • Gave a precise quantitative basis to older and much more vague ideas of atoms • Severed the notion of ‘atomicity’ from its previous metaphysical implications and rendered it into an empirical notion, intimately connected to the notion of ‘elementarity’

Dalton’s chemical atomism represents the first major attempt at reconciling the empirical and quantitative requirements of modern chemistry as advocated by Lavoisier with the theory of discrete particles that compose material bodies and it constitutes one important step in our understanding of the nature of matter. In spite of its flaws and errors, Dalton’s theory succeeded in reconceptualizing atoms in the context of modern chemical science, thus finally divorcing atomism from its ties to early modern metaphysics.

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Notes

1

Hendry, Robin Findlay, “Elements, Compounds, and Other Chemical Kinds”, Philosophy of Science 73 (December 2006), p. 865. 2 Chalmers, Alan, “Atomism from the 17th to the 18th Century”, Stanford Encyclopedia of Philosophy. 3 Chalmers, Alan, “Atomism from the 17th to the 18th Century”, Stanford Encyclopedia of Philosophy. 4 Hendry, Robin Findlay, “Antoine Lavoisier (1743-1794)”, in Philosophy of Chemistry, edited by Andrea I Woody, Robin Findlay Hendry, and Paul Needham, Handbook of the Philosophy of Science Series (The Netherlands: Elsevier, 2012), p. 866. 5 Hendry, Robin Findlay, “Antoine Lavoisier (1743-1794)”, in Philosophy of Chemistry, edited by Andrea I Woody, Robin Findlay Hendry, and Paul Needham, Handbook of the Philosophy of Science Series (The Netherlands: Elsevier, 2012), p. 66. 6 Boas Hall, Marie, “The History of the Concept of Element”, in John Dalton & the Progress of Science (Manchester: Manchester University Press, 1968), p. 21. 7 Chalmers, Alan, “Atomism from the 17th to the 20th Century”, in Stanford Encyclopedia of Philosophy, p. 16. 8 Dalton, John, A New System of Chemical Philosophy, introduction by Alexander Joseph (Manchester: George Wilson, 1827), p. 144. 9 Dalton, John, A New System of Chemical Philosophy, introduction by Alexander Joseph (Manchester: George Wilson, 1827), p. 144. 10 Leicester, Henry M. The Historical Background of Chemistry (New York: John Wiley & Sons, 1961), p. 155. 11 Newman, William R., Atoms and Alchemy: Chymistry & the Experimental Origins of the Scientific Revolution (Chicago: The University of Chicago Press, 2006), p. 221. 12 Bernadette Bensaude-Vincent and Isabelle Stengers, A History of Chemistry, translated by Deborah van Dam (Cambridge, Mass.: Harvard University Press, 1996), p. 114. 13 Knight, David, “John Dalton (1766-1844)”, in Philosophy of Chemistry, edited by Andrea I Woody, Robin Findlay Hendry, and Paul Needham, Handbook of the Philosophy of Science Series (The Netherlands: Elsevier, 2012), pp. 75-76. 14 Knight, David, “John Dalton (1766-1844)”, in Philosophy of Chemistry, edited by Andrea I Woody, Robin Findlay Hendry, and Paul Needham, Handbook of the Philosophy of Science Series (The Netherlands: Elsevier, 2012), p. 76.

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