Chemical atomic theory

1803-1808 Fire and matter theory

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A theory that pictures matter as made of indivisible atoms of a definite weight; compounds are formed in simple whole-number ratios. It explained Proust's law of constant composition and the law of multiple proportions.

The author, the English schoolteacher and meteorologist John Dalton, entered the first list of relative atomic weights in his laboratory notebook on 6 September 1803 and read it to the Manchester Society on 21 October 1803 (printed in 1805). The first full exposition was given by the Scottish chemist Thomas Thomson in 1807, and by Dalton himself in A New System of Chemical Philosophy (part I, 1808).

Atomic weight became a working quantity of chemistry, although its values remained disputed until the international congress at Karlsruhe in 1860.

Why this date

first table of atomic weights in the notebook 6 Sep 1803, paper read 21 Oct 1803 (printed 1805), exposition by T. Thomson 1807, "A New System of Chemical Philosophy" part I May 1808

What grew out of it

• Periodic law

  influenced · Confidence: medium

  The periodic law is the dependence of properties on atomic weight, the quantity introduced by Dalton's atomic theory; but the working values of the weights came from Cannizzaro (1858, Karlsruhe 1860), and Mendeleev explicitly cites them as the basis of the generalisation.

  Dispute: Historians tie the periodic law not to Dalton directly but to Cannizzaro's system of atomic weights after Karlsruhe 1860; Dalton's weight values were largely wrong (rule of greatest simplicity), and for the half-century between 1808 and 1860 the table was impossible because of the confusion of atomic and equivalent weights. What comes from Dalton is the concept of atomic weight itself; the missing link is Cannizzaro's work.

  Link sources

  • Britannica, «Atom», «The beginnings of modern atomic theory» (2024) Verified 20 Sep 2026

    Russian chemist Dmitry Ivanovich Mendeleyev based his system on the atomic weights of the elements as determined by Avogadro's theory of diatomic molecules. In his paper of 1869 introducing the periodic law, he credited Cannizzaro for using 'unshakeable and indubitable' methods to determine atomic weights.

  • Leicester H. M. «Cannizzaro, Stanislao», Dictionary of Scientific Biography (1971) Verified 20 Sep 2026

    It was the recognition of true atomic weights that permitted Meyer and Mendeleev to formulate the periodic law at the end of the 1860's.

  • Mendeleev D., Faraday Lecture 1889 (1889) Verified 20 Sep 2026

    Only such real atomic weights--not conventional ones--could afford a basis for generalisation.

  • Kaji M. «D. I. Mendeleev's Concept of Chemical Elements and The Principles of Chemistry», Bull. Hist. Chem. 27 (1), 4-16 (2002), 4

    In pointing out the inconsistency of Gerhardt's atomic weights of metals and arguing that Cannizzaro corrected them with the 'multiatomicity of metals,' Mendeleev clearly recognized Cannizzaro's successful system of atomic weights.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Unified system of atomic weights (Cannizzaro, Karlsruhe)

  influenced · Confidence: medium

  Cannizzaro kept Dalton's atomic theory and the concept of atomic weight, but replaced the arbitrary rule of simplicity (water as HO) with the derivation of atomic weights from Avogadro's hypothesis and vapour densities, removing half a century of confusion over weights and formulae.

  Dispute: Cannizzaro's immediate support is not Dalton but Avogadro (1811), Ampere, Dumas, Gerhardt and Regnault. No direct assertion of this connection could be found in the historians: Leicester says only that Dalton considered and rejected the equal-volumes hypothesis, and Britannica speaks of the revival of Avogadro's ideas. The well-known passage in the Sunto about the application of Dalton's atomic theory refers not to Cannizzaro himself but to Berzelius, whose atomic weights Cannizzaro was correcting.

  Link sources

  • Leicester H. M. «Cannizzaro, Stanislao», Dictionary of Scientific Biography (via Encyclopedia.com) (1971) Verified 20 Sep 2026

    When Dalton published the first volume of the book explaining his atomic theory in 1808, he considered but rejected the idea that equal volumes of gases under the same conditions contained equal numbers of particles.

  • Cannizzaro S. «Sunto di un corso di filosofia chimica», Il Nuovo Cimento 7, 321-366; Alembic Club Reprint No. 18 (1858) Verified 20 Sep 2026

    influenced by the atomic theory of Dalton (which had been confirmed by the experiments of Wollaston), he applied this theory

  • Britannica, «Atom», «The beginnings of modern atomic theory» (2024) Verified 20 Sep 2026

    Sicilian chemist Stanislao Cannizzaro revived Avogadro's ideas in 1858 and expounded them at the First International Chemical Congress, which met in Karlsruhe, Germany, in 1860.

  • Mendeleev D. «The Periodic Law of the Chemical Elements» (Faraday Lecture 1889), J. Chem. Soc. 55, 634-656 (1889) Verified 20 Sep 2026

    Only such real atomic weights--not conventional ones--could afford a basis for generalisation.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Kinetic theory of gases and statistical mechanics

  influenced · Confidence: medium

  Chemistry gave the kinetic theory a discrete particle with a definite weight, and Maxwell treated the agreement between molecular masses computed from dynamics and the chemists' conclusions as an argument for the real existence of molecules.

  Dispute: No source links Dalton to the kinetic theory directly: Maxwell speaks of 'the deductions of chemists' in general, and the determination of molecular weights from vapour densities is Cannizzaro's subject, not Dalton's. Moreover Brush stresses that their pictures of a gas are opposites: Dalton's particles are almost motionless and surrounded by atmospheres of caloric, he adopted Newtonian repulsion and rejected Gay-Lussac's conclusions ('Dalton explicitly adopted Newton's hypothesis that gas pressure is due to short-range repulsive forces between particles, and envisioned these particles as being surrounded by caloric atmospheres in contact with those of their neighbors'). What the kinetic theory took from chemistry is the discrete particle with a weight, not Dalton's model of a gas.

  Link sources

  • J. C. Maxwell, Atom, Encyclopaedia Britannica, 9th ed., vol. 3 (1875) Verified 20 Sep 2026

    The consistency of this information with the deductions of chemists from the phenomena of combination, greatly strengthens the evidence in favour of the actual existence and motion of gaseous molecules.

  • Klodian Coko (rev. of A. Chalmers), Atomism from the 17th to the 20th Century, Stanford Encyclopedia of Philosophy (2026) Verified 20 Sep 2026

    This legitimated the use of vapour densities for the determination of relative molecular weights. This in turn led to definitive atomic weights and formulae that coincided with those that organic chemistry had yielded by the 1860s.

  • Stephen G. Brush, History of the Kinetic Theory of Gases (Storia della Scienza, vol. 7, ch. 44) (2004) Verified 20 Sep 2026

    This model is radically different from the one proposed at the beginning of the 19th century by the English chemist John Dalton (1766-1844), founder of the modern chemical atomic theory.

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Links under review

• Mass balance and the conservation principle

  prerequisite for · Confidence: medium

  Both sources are summary sentences from Wikipedia articles. The footnote on the first leads to Roscoe H. E., Harden A., «A New View of the Origin of Dalton's Atomic Theory», 1896, and not to the notebook study the sentence reports. Verbatim quotations are needed from Roscoe and Harden and from Dalton J., «A New System of Chemical Philosophy», 1808, ch. II.

  Lavoisier's quantitative chemistry and Proust's law of definite proportions (1797) supplied the weight ratios that Dalton's atomic theory explained through atoms of definite weight; according to Grossman (2021) the theory of 1803 itself arose while reconciling the analytical data of Lavoisier and Cavendish.

  Dispute: The origin of the theory is disputed. Roscoe and Harden (1896), from Dalton's notebooks, and Thackray (Isis 1966) hold that atoms came to Dalton from the physics of gases, not from a search to explain multiple proportions; Grossman (Ambix 2021), from the same notebooks, traces the theory to the reconciliation of the weight data of Lavoisier and Cavendish. Fujii (BJHS 1986) notes that Kapoor denied Proust's influence on Dalton but does not himself find that conclusion decisive. That atomic weights depend on the weight method is uncontested, but no historian has been found who states that Dalton drew on Lavoisier in particular: the chain runs through Proust's law of definite proportions.

  Link sources

  • Britannica, «Atom», «The beginnings of modern atomic theory» (2024) Verified 20 Sep 2026

    English chemist and physicist John Dalton extended Proust's work and converted the atomic philosophy of the Greeks into a scientific theory between 1803 and 1808.

  • «John Dalton Proposes His Atomic Theory and Lays the Foundation of Modern Chemistry», Science and Its Times (2001) Verified 20 Sep 2026

    The chemical revolution due to the work of Antoine Lavoisier (1743-1794) and his circle that had occurred in the last two decades of the eighteenth century had clarified the concept of what elements are, developed a comprehensive and consistent vocabulary of chemistry, and led to the introduction of quantitative methods in chemical investigations.

  • Wikipedia «John Dalton» (2024) Verified 20 Sep 2026

    a recent study of Dalton's laboratory notebook entries concludes he developed the chemical atomic theory in 1803 to reconcile Henry Cavendish's and Antoine Lavoisier's analytical data on the composition of nitric acid, not to explain the solubility of gases in water.

  • Wikipedia «Law of definite proportions» (2024) Verified 20 Sep 2026

    The law of definite proportions contributed to the atomic theory that John Dalton promoted beginning in 1805

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

• Law of definite proportions (Proust)

  influenced · Confidence: medium

  The claim rests on a summary sentence in the Wikipedia article. A verbatim quotation is needed from the work it cites: Dalton J., «A New System of Chemical Philosophy», 1808, ch. II.

  The law of definite proportions gave Dalton's atomic theory a fact which it explained by atoms of definite weight, and according to Britannica Dalton extended Proust's work.

  Dispute: Historians disagree on whether Dalton knew and used Proust's work. Kapoor (1965) and Mauskopf (DSB, 1975): Dalton was in a position to know of Proust and of the controversy with Berthollet, but there is no evidence of Proust's role in the genesis of the theory, and Dalton reached his law from different premises (the physics of gases, per Thackray 1966; the reconciliation of Lavoisier's and Cavendish's data, per Grossman 2021). Fujii (BJHS 1986) finds Kapoor's conclusion not decisive and insists on the interrelation of the two events; Britannica and the textbook tradition say Dalton extended Proust's work. The logical connection between Proust's law and Daltonian atomism was established by Berzelius (1811), not by Dalton himself.

  Link sources

  • Britannica, «Atom», «The beginnings of modern atomic theory» (2024) Verified 20 Sep 2026

    English chemist and physicist John Dalton extended Proust's work and converted the atomic philosophy of the Greeks into a scientific theory between 1803 and 1808.

  • Mauskopf S. H. «Proust, Joseph Louis», Dictionary of Scientific Biography (via Encyclopedia.com) (1975) Verified 20 Sep 2026

    there is no evidence that Proust's work played any role in the genesis of Dalton's chemical atomic theory

  • Fujii K. «The Berthollet-Proust Controversy and Dalton's Chemical Atomic Theory 1800-1820», British Journal for the History of Science 19(2), 177-200 (1986) Verified 20 Sep 2026

    Dalton discovered his law from completely different premises, and does not seem to have got his ideas from Proust.

  • Paradowski R. J. «Proust Establishes the Law of Definite Proportions», EBSCO Research Starters (2023) Verified 20 Sep 2026

    Proust's law was also important in helping to establish the modern atomic theory of John Dalton, even though Dalton himself made only cursory references to Proust in his publications.

  • Wikipedia «Law of definite proportions» (2024) Verified 20 Sep 2026

    The law of definite proportions contributed to the atomic theory that John Dalton promoted beginning in 1805

  "Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Node sources

• Thackray A. «Dalton, John», Dictionary of Scientific Biography (1971) Verified 20 Sep 2026

  And thus it was that this paper closed with the very first list of what we would now call atomic weights.

• Cole-Hamilton D. «2003, A Double Dalton Celebration», Dalton Transactions (2003)

  On 6th September, 1803, John Dalton wrote the first known list of atomic weights in his laboratory notebook and thus started to develop his atomic theory

• AIP Library «Atomic Relations: John Dalton» (2023) Verified 20 Sep 2026

  T.Thomson gave the first full statement in V.III of the 1807 3rd edition of his textbook, A System of Chemistry.

• Britannica, «Atom», «The beginnings of modern atomic theory» (2024) Verified 20 Sep 2026

  A New System of Chemical Philosophy (Part I, 1808; Part II, 1810) was the first application of atomic theory to chemistry.

"Verified" means that on that day the quotation was found at the address given, word for word. No date means we have not been able to open the source yet, not that the quotation is wrong.

Further reading

Not evidence: these carry no quotation and support nothing we wrote. They are books and scans to read next.

• Dalton J. «A New System of Chemical Philosophy», Part I, Manchester (1808)
• Dalton J. «On the Absorption of Gases by Water and other Liquids», Memoirs of the Literary and Philosophical Society of Manchester, 2nd ser., 1, 271-287 (1805)
• Roscoe H. E., Harden A. «A New View of the Origin of Dalton's Atomic Theory», London: Macmillan, 1896; archive.org id newviewoforigino00rosc (1896)
• Thackray A. «The Origin of Dalton's Chemical Atomic Theory: Daltonian Doubts Resolved», Isis 57, 35-55 (1966)
• Grossman M. I. «John Dalton's 'Aha' Moment: the Origin of the Chemical Atomic Theory», Ambix 68(1), 49-71 (2021)

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