Atomic theories, early

In the two decades between Lavoisier s Traite and Daltons New System of Chemical Philosophy, we find a conscious effort to accommodate chemical knowledge to a systematic compositional framework. This assimilation was organized through the new nomenclature and the operational concept of simple body. At the same time, there was a great increase in the gathering of quantitative data and attempts to find rational patterns to incorporate them. The results anticipated empirically the laws of constant composition and multiple proportion that reached full rationality in Dalton s atomic theory early in the next century. 

Medieval alchemists spent years trying to convert other metals into gold without success. Years of failure and the acceptance of Dalton s atomic theory early in the nineteenth century convinced scientists that one element could not be converted into another. Then, in 1896 Henri Becquerel discovered radioactive rays (natural radioactivity) coming from a uranium compound. Ernest Rutherford s study of these rays showed that atoms of one element may indeed be converted into atoms of other elements by spontaneous nuclear disintegrations. Many years later it was shown that nuclear reactions initiated by bombardment of nuclei with accelerated subatomic particles or other nuclei can also transform one element into another—accompanied by the release of radiation (induced radioactivity). 

Original atomic theory (early 1800s) (c) Bohr... 

The concept that all substances are composed of elements and atoms goes back at least 2000 years. Originally, only four elements were recognized air, earth, fire, and water. Each substance was thought to consist of very small particles, called atoms, that could not be subdivided any further. This early mental concept of the nature of matter was extremely prescient, considering there were no experimental results to indicate that matter should be so and none to verify that it was so. Modern atomic theory is much more rigorously based, and we even have the ability to see atoms with special tunneling microscopes. All of chemistry is based on how atoms react with each other. 

The discovery of hafnium was one of chemistry s more controversial episodes. In 1911 G. Urbain, the French chemist and authority on rare earths , claimed to have isolated the element of atomic number 72 from a sample of rare-earth residues, and named it celtium. With hindsight, and more especially with an understanding of the consequences of H. G. J. Moseley s and N. Bohr s work on atomic structure, it now seems very unlikely that element 72 could have been found in the necessary concentrations along with rare earths. But this knowledge was lacking in the early part of the century and, indeed, in 1922 Urbain and A. Dauvillier claimed to have X-ray evidence to support the discovery. However, by that time Niels Bohr had developed his atomic theory and so was confident that element 72 would be a... 

Meinel, Christoph. Early seventeenth-century atomism theory, epistemology, and the insufficiency of experiment. Isis 79 (1988) 68-103. 

The Early Development of the Chemical Atomic Theory," HSPS 9 (1978) 225263, on 249250. 

Nineteenth-century atomic theory could not explain why the aurora exhibits a limited range of specific wavelengths, rather than the full visible spectrum. Early in the twentieth century, however, scientists developed a revolutionary new model of the atom. This model, and the theory that supports it, helped to account for many puzzling phenomena that the existing atomic theory had failed to explain. Among these phenomena are the characteristic colours of the northern lights. 

Since the values in this table are taken from analytical experience, Thomson in effect is predicting the composition of the superacid by the rationale of the atomic theory, but he offers no evidence that the predicted compositions are confirmed by analysis. Early in the next year, however, Thomson delivered a paper on oxalic acid to the Royal Society. The oxalate of potash, he noted, combines with an excess of acid, and forms a superoxalate. The acid contained in this salt is very nearly double of what is contained in oxalate of potash. Suppose 100 part of potash if the weight of acid necessary to convert this quantity into oxalate be x, then xx will convert it into superoxalate. Later he notes that there are two oxalates of... 

Research by the French natural philosophers Joseph-Louis Gay-Lussac and Pierre-Louis Dulong during the early 19 century supported the new atomic theory. That work was done in the laboratory of Claude-Louis Berthollet, the founder of the Societe d Arcueil, near Paris. Berthollet s home is shown in Figure 3. The site of the home today is marked by a plaque, shown in Figure 4. A bust of Berthollet can be found in Arcueil s city hall, the Centre Marius Sidobore. Arcueil itself lies just south of the Boulevard Peripherique that rings Paris. 

For some 50 years after Dalton s atomic theory was published in the early 1800s the theory of chemical bonding made little progress. In the previous section, it was noted that one of the primary functions of... 

The idea that all matter is made of atoms is a familiar concept that that can be recited by the average first grader. However, the general acceptance of the atomic theory dates to the early part of the twentieth century, when Albert Einstein published a paper explaining Brownian motion. The notion of atoms dates back to ancient times, but these models are largely based on philosophical arguments, rather than empirical evidence. John Dalton first formulated an atomic theory... 

In the early years of the nineteenth century, the new chemistry began to bear fruit on both sides of the Channel,270 as well as in other countries, notably in Sweden. The chemical atomic theory proposed by Dalton and developed by Berzelius led to the formulation of the stoichiometric laws of chemical combination and the diligent search for accurate atomic weights. The important link between atoms and electrical charges in the early years of the nineteenth century enabled a new interpretation of chemical combination and the theory of valency. Significant improvements in... 

The way in which atoms join up to form molecules has traditionally been interpreted in terms of the perceived properties and shape of atoms. An early theory of chemical affinity was summarized by Kekule [16], freely translated here, in terms of the concepts atom, molecule, radical and basicity (also called atomicity) ... 

What Lavoisier had said about the unknowability of ultimate elements and the distinction between chemical species and physical atoms continued to trouble a lot of chemists long after the publication of Daltons ideas in the early 180os. Was it possible to reject Daltons chemical atomic theory while adopting everything else that he offered A significant minority of Daltons con-... 

A SHORT HISTORY OF CHEMISTRY (3rd edition), J.R. Partington. Classic exposition explores origins of chemistry, alchemy, early medical chemistry, nature of atmosphere, theory of valency, laws and structure of atomic theory, much more. 428pp. 5X x 8X. (Available in U.S. only) 65977-1 Pa. 10.95... 

One of the early great triumphs of atomic theory was the aufbau principle which explained the periodic table. In it the atomic orbital energies were assigned the following order Is < 2s < 2p < 3s <. ..The occupation number of freeon orbitals was limited to no more than two as was discussed in Section 1. Further Hund s rule was imposed i. e. states of highest spin lie the lowest. The Gel fand state reconstruction of the aufbau for the second row of the periodic table (with mi = +1 or zero) is shown in Fig. 10.1 where 2p+ = + 1,2po = 0 and 2p.i = -1 ... 

In the early 1800s John Dalton formulated his Atomic Theory, which can be summarized as follows ... 

Figure 3.1 John Dalton, early champion of the atomic theory...

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