One-element theories

The modern one-element theory of acids and bases is usually credited to Br0nsted and Lowry. They proposed the proton theory independently in 1923. But G. N. Lewis, who set forth his electronic definitions of acids and bases in the same year, also explained the proton-donor concept as a special case of his broader theory. According to the proton theory, an acid donates a proton to a base, and a base accepts a proton from an acid. The acid and base may be either compounds or ions, as shown in the following examples ... 

Much remains to be done in the way of quantitative measurement as suggested by this new relativity in chemistry. No doubt, as more and more experimental results accumulate, the theory will undergo modification and refinement. Eventually it may give way entirely to another, but the least that can be said for it now is that it can rid chemistry forever of one-element theories of the behavior of matter. This in itself is an accomplishment of considerable magnitude. It opens up our minds as widely as any previous idea in chemistry has ever done. 

As mentioned above, HMO theory is not used much any more except to illustrate the principles involved in MO theory. However, a variation of HMO theory, extended Huckel theory (EHT), was introduced by Roald Hof nann in 1963 [10]. EHT is a one-electron theory just Hke HMO theory. It is, however, three-dimensional. The AOs used now correspond to a minimal basis set (the minimum number of AOs necessary to accommodate the electrons of the neutral atom and retain spherical symmetry) for the valence shell of the element. This means, for instance, for carbon a 2s-, and three 2p-orbitals (2p, 2p, 2p ). Because EHT deals with three-dimensional structures, we need better approximations for the Huckel matrix than... 

The law of multiple proportions This law, formulated by Dalton himself, was crucial to establishing atomic theory. It applies to situations in which two elements form more than one compound. The law states that in these compounds. the masses of one element that combine with a fixed mass of the second element are in a rath of small whole numbers. 

A chain of events in which each link was precision-made. Should international society be any more lenient with men who had exploited the economies of whole countries, aiding and abetting the suffering of millions of people, than any local community was toward the robber who held up the owner of the comer store, took his money, and killed him in the course of the robbery It was, I thought, one element of a very persuasive theory. 

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... 

The fourth century b.c.e. philosopher Plato added four qualities to this theory hot, dry, wet, and cold Two of each of these qualities were shared by each element, as can be seen in Figure 5.2, and because of this shared quality one element could transform into another. Alchemists also related the four qualities and elements to four liquid qualities in the body called humors black bile, phlegm, blood, and yellow bile. They believed that health was attained through the proper balance of these humors. They also believed that an excess of any humor led to... 

Empedocles made no attempt to create a new theory of matter. Instead, he tried to reconcile the thoughts of his various predecessors. He took Thales s theory that everything was made of water and Anaximenes s idea that the primal substance was air, and added two more elements, earth and fire. Empedocles didn t believe that one kind of matter could be transformed into another. Earth couldn t be changed into water, or water into earth, for example. Thus there had to be more than one element. 

When Lavoisier s career as a chemist began, the four-element theory was still widely believed. It was Lavoisier who showed how implausible it really was and who correctly identified many of the elements. He demolished one commonly held belief about water quite early in his career. At the time, it was commonly thought that water could be transmuted into earth. After all, watering plants made them grow. It appeared that water was being transformed into a solid substance. 

The English chemist John Dalton became one of the most famous scientists of the eighteenth century. Although he was known to the public for one idea, that chemical compounds were formed when the atoms of one element joined with the atoms of another, there was much more than this to Dalton s theory. He revolutionized chemistry by emphasizing that atoms have relative weights and that these relative weights can be measured. 

It was a simple picture of matter, as simple as the four-element theory with which chemistry had begun. And it was just as wrong. In fact, in 1925 physicists were already beginning to realize that there were serious problems with this model. For example, the electron was supposed to be approximately the same size as atomic nuclei. How could one confine numerous electrons in so small a space Uranium, for example, was supposed to have 238 protons and 146 electrons within the nucleus. 

This syndrome is generally referred to as disharmony between the Liver and Spleen. In fact, it can be divided into several sub-syndromes besides disharmony between the Liver and Spleen, such as disharmony between the Liver and Stomach, and disharmony between the Liver and Large Intestine. Since the Stomach and Large Intestine are directly finked to the transportation function of the Spleen, and both belong to Earth in the Five-Element theory, the liver often attacks these organs if it overacts on the Spleen. Hence they are often considered and discussed as one syndrome under the name of disharmony between the Liver and Spleen. 

We have already seen in Chapter 2 that everything you see around you is made out of tiny particles called atoms (Figure 3.1). When John Dalton developed his atomic theory, about 200 years ago (1807/1808), he stated that the atoms of any one element were identical and that each atom was indivisible . Scientists in those days believed that atoms were solid particles like marbles. 

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. 

Following this theory, the transformation of one element into another one was realized. The nuclear equation of this artificial radioactive reaction is illustrated below ... 

Dalton s Atomic Theory was an important milestone in the development of chemistry, but modern chemistry students will correctly note that it was incomplete, and in some cases, just plain wrong. For example, not all atoms of a given element are identical, because Dalton did not know about the existence of isotopes. Likewise, we now know that atoms are comprised of still smaller particles and that nuclear processes convert atoms of one element into atoms of other elements. By the very nature of science, when a hypothesis, law or model—no matter how dearly held—fails to make correct predictions, it must be discarded or modified. So, significant portions of Dalton s original theory have been modified. However, the importance of Dalton s theory can hardly be understated and should not be assessed by whether or not it was correct in the finest details, but in how it provided a working foundation that guided current and future scientists in their quest to understand the physical world. 

In 1661 Boyle published The Sceptical Chymist, which demolished what he regarded as either fallacious reasoning or incompetent experiment or both. It was above all an attack on theories of the elements devised by those seduced more by theory than by experimental evidence. We have already encountered the principal element theories that Boyle attacked. Aristotelians had their four elements, earth, air, fire, and water. Paracelsians had three, the tria prima of Mercury, Sulfur, and Salt, which were not the same as the common mercury, sulfur, and salt of the laboratory, apothecary s shop, or even (in the case of table salt) the kitchen. Van Helmont had either one or two, depending on how you interpreted him water, or, taking the biblical account literally, water and air,... 

We have seen that one of Boyle s major concerns was to reveal the inner workings of nature and that he considered chemical analysis to be one way to pursue this goal. Fire provided the commonest means of analysis, and Boyle was determined to show that, when applied to the various element theories of his day, it failed singularly to provide support for any of them. If one burned wood, ash and soot were produced, and so was smoke. This was not helpful... 

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