Download 6. Early Atomism - UZH - Department of Chemistry

History of Chemistry
Organisch-chemisches Institut
Universität Zürich
Professor Ramberg
Modern Atomic Theory: Davy, Dalton, and Berzelius
The modern version of the atomic theory effectively began with John Dalton’s method
of calculating atomic weights, which he published in several places between 1805 and
1808. During the first two-thirds of the nineteenth century, there were several
competing sets of atomic/equivalent weights until chemists came to agreement during
the 1860s.
I. Current Electricity
1. Luigi Galvani
2. Alessandro Volta
3. William Nicholson and the decomposition of water, 1800
II. Humphry Davy (1778-1829)
1. Background
2. The role of the Voltaic Pile
3. Electrolysis of soda and potash
4. The muriatic acid radical
5. Elements, atoms, and simple substances
III. John Dalton (1766-1844)
1. Background
2. Dalton’s Atomic Theory
3. Influences
a. Isaac Newton
b. Chemical combining proportions
c. Composition of the atmosphere
d. Solubility of gases in water
“On the Absorption of Gases by Water” Memoirs of the Literary and
Philosophical Society of Manchester (1805)
1. All gases that enter into water and other liquids by means of pressure, and
are wholly disengaged again by the removal of that pressure, are
mechanically mixed with the liquid, and not chemically combined with it.
2. Gases so mixed with water, etc. retain their elasticity or repulsive power
amongst their own particles, just the same in the water as out of it, the
intervening water having no other influence in this respect than a mere
vacuum.
3. Each gas is retained in water by the pressure of gas of its own kind
incumbent on its surface abstractedly considered, no other gas with which it
may be mixed having any permanent influence in this respect.
…
8. The greatest difficulty attending the mechanical hypothesis, arises from
different gases observing different laws. Why does water not admit its bulk of
every gas alike? This question I have duly considered, and though I am not
yet able to satisfy myself completely, I am nearly persuaded the circumstance
depends upon the weight and number of the ultimate particles of the several
gases: those whose particles are lightest and single being the least
absorbable, and the others more according as they increase in weight and
complexity. An enquiry into the relative weights of the ultimate particles of
bodies is a subject, as far as I know, entirely new: I have lately been
prosecuting this enquiry with remarkable success. …
4. A New System of Chemical Philosophy (1808)
Chapter II, “On the Constitution of Bodies”
Whether the ultimate particles of a body, such as water, are all alike, that, if
the same figure, weight, etc. is a question of some importance. From what is
known, we have no reason to apprehend a diversity in these particulars: if it
does exist in water, it must equally exist in the elements constituting water,
namely, hydrogen and oxygen. … Therefore we may conclude that the
ultimate particles of all homogeneous bodies are perfectly alike in weight,
figure, etc. In other words, every particle of water is like every other particle of
water; every particle of hydrogen is like very other particle of hydrogen, etc.
Chapter III, “On chemical synthesis”
… In all chemical investigations, it has justly been considered an important
object to ascertain the relative weights of the simples which constitute a
compound. But unfortunately the enquiry has terminated here; whereas from
the relative weights in the mass, the relative weights of the ultimate particles
or atoms of the bodies might have been inferred, from which their number and
weight in various other compounds would appear, in order to assist and to
guide future investigations, and to correct their results. Now it is one great
object of this work, to shew that 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 in
to the formation of one more compound particle.
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; namely
1 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 atom of B = 1 atom of F, quaternary.
3 atom of A + 1 atom of B = 1 atom of G, quaternary.
The following general rules 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.
2d. When two combinations are observed, they must be presumed to be a
binary and a ternary.
3d. When three combinations are obtained 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.
[three more principles]
From the application of these rules, to the chemical facts already well
ascertained, we deduce the following conclusions: 1st. that water is a binary
compound of hydrogen and oxygen, and the relative weights of the two
elementary atoms are as 1:7, nearly; 2d. That ammonia is a binary compound
of hydrogen and azote, and the relative weights of the two atoms are as 1:5,
nearly; 3d. That nitrous gas is a binary compound of azote and oxygen, the
atoms of which weigh 5 and 7 respectively … [two more cases] In all these
cases the weights are expressed in atoms of hydrogen, each of which is
denoted by unity. …
IV. Jakob Berzelius (1779-1848)
1. Background
2. Importance of Electrochemistry
3. Centrality of oxygen
4. Atoms are the cause of chemical proportions
“Essay on the Cause of Chemical Proportions, and on Some Circumstances
Relating to Them: Together with a Short and Easy Method of Expressing
Them,” Annals of Philosophy (1814)
The fact that bodies combine in definite proportions when other forces do not
oppose their re-union, added to the observation that when two bodies, A and
B, combine in different proportions, the additional portions of the one are
always multiples by whole numbers, 1, 2, 3, 4, &c. lead us to conclude the
existence of a cause in consequence of which all other combinations become
impossible. Now what is that cause? It is obvious that the answer to this
question must constitute the principal basis of chemical theory.
When we reflect on this cause it appears at first evident that it must be of a
mechanical nature; and what presents itself as the most probable idea, and
most conformable to our experience, is, that bodies are composed of atoms,
or of molecules, which combine 1 with 1, 1 with 2, or 3, 4, &c.; and the laws of
chemical proportions seem to result from this with such clearness and
evidence, that it seems very singular that an idea so simple and so probable
has not only not been adopted, but not even proposed before our own days.
As far as I know, the English philosopher, Mr. John Dalton, guided by the
experiments of Bergman, Richter, Wenzel, Berthollet, Proust, and others, was
the first person who endeavoured to establish that hypothesis.
5. Electrochemical Dualism
6. Berzelian notation and its significance
I must observe here that the object of the new signs is not that, like the old
ones, they should be employed to label vessels in the laboratory: they are
destined solely to facilitate the expression of chemical proportions, and to
enable us to indicate, without long periphrases, the relative number of
volumes of the different constituents contained in each compound body. By
determining the weight of the elementary volumes, these figures will enable
us to express the numeric result of an analysis as simply, and in a manner as
easily remembered, as the algebraic formulas in mechanical philosophy.
(1814)
... for example, 2 SO3 + CuO2 = persulphate of copper; The number 2 denotes
that the acid in the salt contains not only two particles of sulphur but six of
oxygen, etc.
V. Combining Volumes--an alternative to Atomic Weights
1. Joseph Louis Gay-Lussac (1778-1850)
2. Amedeo Avogadro (1776-1856)
Further Reading
Theron Cole, Jr, “Dalton, Mixed Gases, and the Origin Of the Chemical Atomic
Theory,” Ambix, 25 (1978): 117-30
Gillian Gass, “Spheres of Influence: Illustration, Notation, and John Dalton’s
Conceptual Toolbox, 1803-1835,” Annals of Science, 64 (2007): 349-82
Alan J. Rocke, “In Search of El Dorado: John Dalton and the Origins of the
Atomic Theory,” Social research, 72 (2005): 125-57
Robert Siegfried, “The Discovery of Potassium and Sodium, and the Problem of
the Chemical Elements,” Isis, 54 (1963): 247-58
Arnold W. Thackray, “The Emergence of Dalton’s Chemical Atomic Theory:
1801-08,” The British Journal for the History of Science, 3 (1966): 1-23