modern atomic theory: dalton, davy and berzeliusffffffff-e65b-5674-ffff...dalton’s atomic theory...

Modern Atomic Theory: Dalton, Davy and Berzelius

Monday, October 4, 2010

Issues in Early Modern Atomism

• Can chemistry be mathematized? • Are there laws that govern chemical composition?• Are Lavoisier’s “simple substances” elementary? • How can we probe the world of the invisibly small?• Do the empirically derived laws of chemical proportions indicate a

corresponding microworld of atoms and molecules?


Alessandro Volta (1745-1828)Luigi Galvani (1737-1798)


Alessandro Volta, “On the Electricity excited by the mere contact of conducting substances of different kinds,” Philosophical Transactions of the Royal Society of London, Vol. 90. (1800), pp. 403-431.


Humphry Davy (1778-1829)Monday, October 4, 2010

John Dalton (1766-1844)Monday, October 4, 2010

Dalton’s Atomic Theory

• Water is composed of 12.5% hydrogen and 87.5% oxygen by weight (a 1:7 ratio)

• The water “molecule” must reflect this composition at the microscopic level.

• Therefore, if water is composed of one hydrogen atom, and one oxygen atom, then the oxygen atom must be seven times heavier than the hydrogen atom.

• In carbonic acid gas, assuming one atom of carbon and one atom of oxygen, if oxygen is seven then carbon is 5.4.

• in olefiant gas, the weight ratios of hydrogen to carbon indicate carbon has a weight of 5.4 times that of hydrogen (carbon’s weight can be derived in two separate ways).


Influences on Dalton

Isaac Newton, Book 2 of the Principia Mathematica:

In a gas that obeys Boyle’s law, the repulsive force between the particles of that gas must be inversely related to the distance between them (provided such particles exist)


Influences on DaltonIsaac Newton, 31st Query of the Opticks:

it seems probable to me, that God in the Beginning form'd Matter in solid, massy, hard, impenetrable, moveable Particles, of such Sizes and Figures, and with such other Properties, and in such Proportion to Space, as most conduced to the End for which he form'd them; and that these primitive Particles being Solids, are incomparably harder than any porous Bodies compounded of them; even so very hard, as never to wear or break in pieces ...



Chemical combining proportions:• “Carburetted hydrogen”• “Olefiant gas”• Nitrogen oxides



Chemical combining proportions:• “Carburetted hydrogen”• “Olefiant gas”• Nitrogen oxides

Composition of the atmosphereSolubility 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.


“On the Absorption of Gases by Water” Memoirs of the Literary and Philosophical Society of Manchester, (1805)

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. …


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.

. 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.



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.


Jöns Jakob Berzelius (1779-1848)Monday, October 4, 2010

“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.


“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)

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.


Berzelian Notation

The chemical signs ought to be letters, for the greater facility of writing, and not to disfigure a printed book. I shall take, therefore, for the chemical sign, the initial letter of the Latin name of each elementary substance: but as several have the same initial letter, I shall distinguish them in the following manner:-- 1. In the class which I call metalloids, I shall employ the initial letter only, even when this letter is common to the metalloid and some metal. 2. In the class of metals, I shall distinguish those that have the same initials with another metal, or a metalloid, by writing the first two letters of the word. 3. If the first two letters be common to two metals, I shall, in that case, add to the initial letter the first consonant which they have not in common: for example, S = sulphur, Si = silicium, St = stibium (antimony)[2], Sn = stannum (tin), C = carbonicum, Co = cobaltum (cobalt), Cu = cuprum (copper), O = oxygen, Os = osmium, &c“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)


Berzelian Notation

The chemical sign expresses always one volume of the substance. When it is necessary to indicate several volumes, it is done by adding the number of volumes: for example, the oxidum cuprosum (protoxide of copper) is composed of a volume of oxygen and a volume of metal; therefore its sign is Cu + O. The oxidum cupricum (peroxide of copper) is composed of 1 volume of metal and 2 volumes of oxygen; therefore its sign is Cu + 2O. In like manner, the sign for sulphuric acid is S + 3O; for carbonic acid, C + 2O; for water 2H + O, &c.

“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 Meanings of Berzelian Notation

Berzelius (1814):

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.

... 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.


The Meanings of Berzelian Notation

• abbreviations for composition• notation for empirically derived stoichiometric relationships • signs that represent individual particles in combination (ontological

commitment to atoms)• Chemists can adopt one or more of these meanings simultaneously. • Berzelian formulas serve as “paper tools” in themselves for constructing

knowledge about chemical composition.


Joseph Louis Gay-Lussac (1778-1850)Monday, October 4, 2010

Combining Volumes

2 volumes hydrogen + 1 volume oxygen –––> water3 volumes hydrogen + 1 volume nitrogen –––> ammonia

Assumption:

Equal volumes of gas contain equal numbers of atoms

Then the formula for water must be H2O, changing the atomic weight scale.


Amedeo Avogadro (1776-1856)Monday, October 4, 2010

modern atomic theory: dalton, davy and berzeliusffffffff-e65b-5674-ffff...dalton’s atomic theory...

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