Atomic theory, beginnings

Trace the history of the development of atomic theory, beginning with Dalton. 

For two thousand years atoms were considered the smallest and indivisible units of nature. At the beginning of the nineteenth century Dalton got chemistry on the path of atomic theory with his book, A New System of Chemical Philosophy, in which he argued that unbreakable atoms form compounds by linking with other atoms in simple... 

At the beginning of this course you were a new tenant. You were told that chemists believe in atoms and you were asked to accept this proposal tentatively until you yourself knew the evidence for it. Since that time, we have used the atomic theory continuously in our discussions of chemical phenomena. The atomic theory passes the test of a good theory it is useful in explaining a large number of experimental observations. We have become convinced there are atoms. 

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. 

Johnstone (2000) emphasises the importance of beginning with the macro and symbolic levels (Fig. 8.3) because both comers of the triangle are vistrahsable and can be made concrete with models (p. 12). The strb-micro level, by far the most difficult (Nelson, 2002), is described by the atomic theory of matter, in terms of particles such as electrorrs, atoms and molecules. It is commorrly referred to as the molecular level. Johnstone (2000) describes this level simirltaneorrsly as the strength and weakness of the subject of cherrristry it provides strength through the intellectual basis for chemical explanatiorrs, but it also presents a weakness when novice students try to learn and rmderstand it. 

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... 

Only fragments of the writings of the founders of the atomic theory have come to us. The views of these philosophers are preserved, and doubtless amplified and modified, in a Latin poem. Concerning the Nature of Things, written by Lucretius, who was bom a century before the beginning of our era. Let us consider the picture given in that poem of... 

William B. Jensen begins the volume with an overview of scientific atomic theories from the 17 through 20 centuries. He mentions ancient atomism, but he begins in earnest analyzing corpuscular theories of matter proposed or entertained by natural philosophers in the 17 century. He describes the dominant flavors of atomic notions over fom centuries, from the mechanical through the dynamical, gravimetric, and kinetic, to the electrical. Jensen is Oesper Professor of Chemical Education and History of Chemistry at the University of Cincirmati and was the foimding editor of the Bulletin for the History of Chemistry. 

The first name which appears to represent a chemical expert whose writings have been preserved fragmentarily in quotations or copies by later writers, is that of Democritus. This person is generally called by alchemical writers Democritus of Abdera, the philosopher who first enunciated an atomic theory. Internal and external evidence, however, make it clear that Democritus, the alchemist, has little in common with the philosopher of Abdera, and that this psuedo-Democritus lived at about the beginning of our era and belonged to the Alexandrian school of neoplatonists. The exact time of his life is unknown. H. Kopp10 considered that his work, Physica et Mystica, was written not earlier than the third century A.D. 

The British scientist John Dalton put forward an atomic theory of matter at the beginning of the nineteenth century. This remains a sound basis for understanding the world around us and the actions and reactions of its chemical components. Dalton proposed that all substances are made of matter, which occupies space and has mass, and his theory deals with the nature of this matter. 

If you recall from the beginning of this chapter, some of the work that led to the development of the modem atomic theory was done by scientists Max Planck, Albert Einstein, Louis de Broglie, Werner Heisenberg, Niels Bohr, and Erwin Shrodinger. The first work centered around light (electromagnetic radiation), while the later work focused on the wave-like nature of matter. The AP test does not probe too deeply into the theoretical considerations of any of these scientists, but some calculations have popped up on previous tests. Therefore, let s turn our attention to some of the equations associated with these scientists work. 

Emergence of chemical atomism. The beginning of the 19th century was marked by the emergence of atomic theory developed by the famous English scientist John Dalton (1766-1844). According to Dalton, atoms combine in multiple proportions. Thus, if two atoms form only one compound, they associate in the 1 1 ratio if two atoms form two compounds, their ratios in these compounds are respectively 1 1 and 1 2, and so on. Accordingly, Dalton adopted the formula HO for water, CO for carbon monoxide, COg for carbon dioxide, and so on. From these formulas he determined the atomic masses of elements. It is clear that frequently both atomic masses and chemical formulas of Dalton were not correct. 

In Chap. 3 the elementary structure of the atom was introduced. The facts that protons, neutrons, and electrons are present in the atom and that electrons are arranged in shells allow us to explain isotopes (Chap. 3), chemical bonding (Chap. 5), and much more. However, with this simple theory, we still have not been able to deduce why the transition metal groups and inner transition metal groups arise, and many other important generalities. In this chapter we introduce a more detailed description of the electronic structure of the atom which begins to answer some of these more difficult questions. 

It s impossible to weigh or isolate a single atom. We know that the atom is so tiny that we cannot feel it by using our senses. Therefore, the development of atomic theories have been based on indirect methods. At the beginning of the 19 century, the existence of atoms had been a point of contention. Erstwhile, Muslim scientist Jabir Bin Hayyan (721-815) had discovered that an individual atom could be split to release a huge amount of energy. 

Even as late as the beginning of the twentieth century, when the development of the kinetic theory of gases had added its strong support of the atomic theory to that of the... 

Although the concept of the atom was revived in the 18 century, it took the passing of another hundred years before significant progress was made. The work done in the 19 century by John Dalton (1766-1844), a schoolteacher in England, marks the beginning of the development of modern atomic theory. Dalton revived and revised Democritus s ideas based upon the results of scientific research he conducted. The main points of Dalton s atomic theory are shown in Figure 4-4. 

The acceptance of atomic theory was only the beginning of our understanding of matter. Once scientists were fairly convinced of the existence of atoms, the next set of questions to be answered emerged. What is an atom like How are atoms shaped Is the composition of an atom uniform throughout, or is it composed of still smaller particles While many scientists researched the atom in the 1800s, it was not until almost 1900 that answers to some of these questions were found. The next section explores the discovery of subatomic particles and the further evolution of atomic theory. 

Whose work is credited with being the beginning of modem atomic theory (4.1)... 

Dalton s atomic theory (p. 89) Atheory proposed by John Dalton in 1808, based on numerous scientific experiments, that marked the beginning of the development of modem atomic theory. 

The atomic theory was the work of the nineteenth century beginning with the original publication of John Dalton6 in Manchester and undisputed acceptance with the Nobel-prizing winning explanation of Brownian motion1 published by Albert Einstein8 one hundred years ago in 1905.1... 

We shall now investigate the question of how the statements of the atomic theory with regard to the values of the terms are to be corrected in the light of the recognition of the existence of spin. We begin with the simple example of the hydrogen atom, and with the schemes of terms which may be called hydrogen-like (alkali terms, X-ray terms). In Chapter V (pp. 112, 126) we discussed the values of... 

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