Atomic theory definition

Let us begin by looking again at the kinds of evidence we already have for the existence of atoms—the evidence from chemistry. We shall consider, in turn, the definite composition of compounds, the simple weight relations among compounds, and the reacting volumes of gases. Each behavior provides experimental support for the atomic theory. 

The atomic theory provides a ready explanation for the definite composition of chemical compounds. It says that compounds are composed of atoms, and every sample of a given compound must contain the same relative number of atoms of each of its elements. Since the atoms of each element have a characteristic weight, the weight composition of a compound is always the same. Thus, the definite composition of compounds provides experimental support for the atomic theory. 

Modem atomic theory teaches that an atom is made up of positively charged protons, an equal number of negatively charged, i much, much tinier electrons, and varying numbers of uncharged j neutrons. Each element has a definite number of protons, and no other element can have that same number. For example, the element hydrogen has one, helium has two, lithium, three, and so on. The number of protons in the nucleus, or center, of each atom, is called the atomic number of the element. 

Loring published chemistry books—Studies in Valency (1913), Atomic Theory (1921), Definition of the Principle of Equivalence (1922), and The Chemical Elements (1923). During the brief existence of the Alchemical Society, he published twenty articles (eight of them lead articles) in Chemical News on such subjects as atomic weight, the radio-atoms, the evolution of chemical elements, and a five-part Introduction to the Theory of Relativity. He also published seven correspondences in the journal, and Chemical News reviewed his Studies in Valency positively. 

At the beginning of the nineteenth century, John Dalton (see plate 15 (sic should be 16 ) put forward his Atomic Theory in explanation of these facts. This theory assumes (1) that all matter is made up of small indivisible and indestructible particles, called "atoms" (2) that all atoms are not alike, there being as many different sorts of atoms as there are elements (3) that the atoms constituting any one element are exactly alike and are of definite weight and (4) that compounds are produced by the combination of different atoms. Now, it is at once evident that if matter be so constituted, the stoichiometric laws must necessarily follow. For the smallest particle of any definite compound (now called a "molecule") must consist of a definite assemblage of different atoms, and these... 

There are also certain other facts which appear to demand such a modification of Dalton s Atomic Theory as is found in the Electronic Theory. One of the characteristics of the chemical elements is that each one gives a spectium peculiar to itself The spectrum of an element must, therefore, be due to its atoms, which in some way are able, at a sufficiently high temperature, to act upon the ether so as to produce vibrations of definite and characteristic wave-length. Now, in many cases the number of lines of definite wavelength... 

The Bohr theory of atomic structure allotted to each extra-nuclear electron within the atom a definite geometrical orbit and, more important, associated with each orbit a fixed total energy value. 

In your notebook, list the main ideas in Dalton s atomic theory. Explain how this theory enabled chemists to explain the three mass laws the law of conservation of mass, the law of definite proportions, and the law of multiple proportions. 

The coupled cluster calculations involved in Wlc theory were carried out using MOLPRO 2002.3. (7P) (For the open-shell calculations on the constituent atoms, the definition of the open-shell CCSD and CCSD(T) energies in Ref. (20) was employed.) The density functional calculations were carried out using a modified version of Gaussian 98 rev. All (27), as were the Gn theory (22-24) and CBS-n (25) calculations. 

Dalton s atomic theory 11 Dangling bond on Si(lOO) 18 Si(lll), on 13 DAS model 12—18 dc dropoff method 282 Decay constant definition 5... 

NE OF THE CENTRAL THEMES of this book is to show how the development of the concept of neutral salt in the eighteenth century made possible the creation of a compositional nomenclature by L.-B. Guyton de Morveau in 1782, which when adapted to the new chemistry of Lavoisier led to the creation of a definition of simple body the material element. The second major theme then describes how this new chemistry led to the final development of modern chemical composition in its atomic structure introduced by John Dalton. His atomic theory contained the symbolic operators that furnished the most convenient representation of the material composition of bodies that had become available by the end of the eighteenth century. The idea of an individual atomic weight unique to each element depended most immediately upon the concept of simple body, introduced by the authors of the M thode de nomenclature chimique in 1787. The new nomenclature was itself based on the principle that a name of a body ought to correspond to its composition. 

Most chemists at that time would hardly have found Berthollets view of variable composition a welcome idea, but even the acceptable (and empirically derived) chemical rules, such as definite proportions, needed a rational justification. Daltons atomic theory in 1808, like that of Berthollet, came from outside the mainstream of the empirical chemical story that this account has been following, but it produced so functional a rationale for the explicit laws of chemical composition, that the whole dispute regarding definite or indefinite composition became moot. 

Sala was also an important champion of the introduction of the chemical medicines. Sala s description of fermentation, as an intimate movement of elementary particles which tend to group themselves in a different order to make new compounds, is evidence of a concept doubtless derived from the atomic theory of the Greeks, and differs from the concept of chemical action in the nineteenth century mainly by lacking qualitative and quantitative definition. 

The atomic theory as originally conceived by Democritus and Epicurus, developed by Lucretius, and resurrected by Gassendi from about 1647 on, was doubtless the source from which Boyle derived his ideas on this subject, as he cites both Epicurus and Gassendi. Boyle, however, in the above proposition carefully avoids any dogmatic assertion of these hypotheses. It is plain, however, that these atoms or corpuscles as he calls them are a constant element of his thought. In part six (an appendix) to the Sceptical Chymist, he states more distinctly his definition of a chemical element. Carneades says 80... 

Two quantities, represented by commuting operators, possess definite values at the same time. In atomic theory it is very important to find a full set of commuting operators and wave functions, because in this case we can unambiguously describe the system considered. Having defined a full set of wave functions xpt (i = 1,2we are in a position to expand the function of arbitrary state xp in terms of linear combination of these functions of the system considered, i.e. 

How does Dalton s atomic theory account for the law of mass conservation and the law of definite proportions ... 

In 1799 Joseph Proust (1754-1826), a French chemist, observed that specific compounds always contained the same elements in the same ratio by mass. This came to be known as the law of definite proportions. The law of definite proportions provided a means for determining relative weights for numerous atoms and verified John Dalton s theory that elements are made up of atoms. Dalton (1766-1844) was an English teacher, chemist, and physicist. He used modern scientific methodology to develop long-lasting atomic theories. 

In 1808 John Dalton proposed his atomic theory, which included the statement that when atoms of two or more elements combine to form a compound, they combine in a definite ratio by number of atoms and by mass. This is called the law of definite proportions. This provided a means to determine the mass of one atom relative to another. It was necessary to assign a mass to one element to find the mass of another element in a compound. Today we use the most common carbon isotope, assigned a mass of 12.00 atomic mass units (amu), as the basis for comparative weights of the atoms. 

Pure aluminum oxide always contains 52.9% Al, 47.1% O, an example of the Law of Definite Proportions. This empirical law applies to almost all chemical compounds and was of great importance in the acceptance of Dalton s atomic theory. 

Faraday was thus able to enunciate his two laws of electrolysis. His second law implied that both matter and electricity were atomic in nature. Faraday was deeply opposed to atomism, especially the theory proposed by John Dalton, and indeed held a very antimaterialist view. It was clear to Faraday, however, that the law of definite proportions also required some sort of atomic theory. What Faraday proposed in the 1840s was that matter was perceived where fines of force met at a particular point in space. A direct experimental outcome of this radical theory was Faraday s discovery in 1845 of the magneto-optical effect and diamagnetism. The field theory that Faraday developed from this was able to solve a number of problems in physics that were not amenable to conventional approaches. This was one reason why field theory was taken up quite quickly by elite natural philosophers such as William Thomson (later Lord Kelvin) and James Clerk Maxwell. 

Corpuscles might well be divisible, but atoms by definition were not. Today, we associate atoms with chemical elements. Boyle definitely did not do so. That made for difficulties in relating theory to laboratory practice, for reasons we shall soon see. 

Suppose for example one atom of element A combines with one atom of element B, to form the compound AB then, since the weights of atoms of the same element are always alike and since whatever amount of the compound is taken it always contains an equal number of atoms of each element, the proportion by weight of the two elements must always be the same in this compound. Thus the law of definite proportions is a necessary deduction from the atomic theory. Let it be understood, however, that the law is a fact established by careful measurements. The theory is simply the best effort of the human mind to furnish an explanation of the facts. 

The reasoning is similar for the law of multiple proportions. Suppose that one atom of A can combine with two atoms of B in forming an entirely different, but none the less definite, compound. Let us designate this compound AB2. The law of definite proportions would hold for this compound as well as for the first. Furthermore, if we should take such amounts of each compound that each contained the same number of atoms of A then the second would contain twice as many atoms of B as the first. The weight of B in the second would, therefore, be exactly twice the weight of B in the first compound. Thus the law of multiple proportions is also a necessary deduction from the atomic theory. 

A firm believer in the atomic theory of Dalton, Berzelius made his new symbols stand for the relative atomic weights of the atoms. The initial letter capitalized represented one atom of the element. The symbols stood for definite quantitative measurements and enabled us to indicate without long periphrases the relative number of atoms of the different constituents present in each compound body. Thus they gave a clue to the chemical composition of substances. This was a tremendous step toward making chemistry a mathematical science. 

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