Historical Outline

3 Radii of Atoms in Molecules and Crystals 1.3.1 Historical Outline 

The concept of the atomic radius was introduced in 1920 by Bragg [104], who estimated the radii for some 40 elements from the few structures then known. Later, Slater [105] used a more extensive experimental basis (1200 crystal sttuctures of various chemical types) to compile a table of atomic radii for 95 elements, which 

It should be noted, that the term radius implies that atoms are considered as hard spheres, which touch each other when atoms are bonded, but can not penetrate or deform each other. This image seems to contradict the concepts of quantum mechanics, as the electron clouds of atoms have no clear-cut boundaries and must overlap to form a chemical bond. However, one must keep in mind that (i) the repulsion which prevents closer approach of atoms, is due mainly to Pauli exclusion which forbids electrons with similar spins to occupy the same space, and (ii) the electron cloud of an atom (other than H or He) comprises two distinct parts the dense core and the much more diffuse valence electron clouds, with a steep jump of electron density between the former and the latter (Fig. 1.5). For these reasons, the repulsive force increases very steeply with the decrease of d, and the overlap of valence shells of chemically bonded atoms is limited in practice to area where the electron density does not exceed ca. 10 % of the maximum [37]. Furthermore, since core electrons are unaffected by chemical bonding, the atomic radius can be regarded in the first approximation as the constant of a given element, invariant against the composition and structure of the solid. 

In the first place, atomic radii have been diversified into metallic and covalent radii, the latter applied to all structures other than metallic. These structures being very diverse in character, the radii obtained by different authors vary widely depending on the data basis used and the simplifying assumptions made. In fact, the metallic and covalent bonds are basically similar, both implying complete sharing of valence electrons indeed, the metallic bonding is often described as non-directional covalent. As will be shown below, there is a basic unity between all systems of metallic and covalent radii most of the differences between them can be attributed to the differences in the coordination number (tVc), bond polarity and valence (oxidation state). The atomic radius always increases with N, the increase is related to the parallel decrease of the ionization potential. 

The decrease of Z in a solid is caused by multi-particle (extra valence) interaction of atoms within the coordination sphere, which can be described as external screening [106], 

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An historical outline has been presented of some of the important developments in the study of luminescence, which reveals that most of the theory and practise used today were already in place by 1930. This is followed by a selection of recent developments in applications of luminescence intended to suggest to the reader possible uses of this versatile research tool in his own research. 

The above historical outline refers mainly to the EPR of transition ions. Key events in the development of radical bioEPR were the synthesis and binding to biomolecules of stable spin labels in 1965 in Stanford (e.g., Griffith and McConnell 1966) and the discovery of spin traps in the second half of the 1960s by the groups of M. Iwamura and N. Inamoto in Tokyo A. Mackor et al. in Amsterdam and E. G. Janzen and B. J. Blackburn in Athens, Georgia (e.g., Janzen 1971), and their subsequent application in biological systems by J. R. Harbour and J. R. Bolton in London, Ontario (Harbour and Bolton 1975). 

Perhaps the most noteworthy of this brief historical outline is that all the cited dates are from more than a quarter century ago. Of course, this is not to imply that nothing has happened since in terms of theoretical or technological developments, but the message is that EPR in general, and bioEPR in particular, is a mature spectroscopy, whose application readily pays off if you just take the trouble of getting acquainted with its now-well-defined requirements, possibilities, and limitations. 

Scales and Weights, a Historical Outline by Bruno Kisch, Yale University Press, New Haven and London, 1965. Good historical background on the development of weights and weighing. 

By way of introduction I need to do two things. The first is to provide a historical outline of the life of James Watt, a general overview that will assist in situating my specific, and rather specialized, argument about the centrality of chemistry to his life and work. The second is to explain the structure and the strategy of my study, as well as some of the basic assumptions that underlie it. 

Starting the schematical historic outline now, one can suppose ETO integral calculation starts with the pioneering work of Hylleraas [3], Kemble and Zener [4], Bartlett [5], Rosen [6], Hirschfelder [7], Coulson [8] and Ldwdin [9], solidifying as a quantum chemical discipline with the publication of overlap formulae and tables by MuUiken et al. [10]. 

Wintermeyer, U. The Root of Chromatography Historical Outline of the Beginning to Thin Layer Chromatography, GIT Verlag, Darmstadt, 1989. 

Nriagu JO Saturnine drugs and medicinal exposure to lead an historical outline, in Human Lead Exposure. Edited by Needleman HL. Boca Raton, FL, CRC Press, 1992, pp 3-21... 

A historical outline of Chinese chemistry (The ancient period)]. Beijing ... 

The literature is filled with reports on dust explosion incidents, some of them with disastrous consequences. In his book Explosions , Bartknecht provides a short historical outline of first reports describing dust explosions and milestones of their research [79]. According to this survey, one of the first reports dates back to 1785 and describes the destruction of a flour storage building. In general, most accidents occurred in either the food or the mining industry. In 1844 Faraday discovered, that coal dust is explosible. 

Praxair Historical Outline Manuscript Praxair Heritage Center Collection, Tonawanda, NY, undated. 

A brief historical outline of work on three species, R. japonica, R, trichocarpa and R, umbrosa var. leucantha f. kameba is presented in the following paragraphs. 

Quartermain LB (1964) The BaUeny Islands A descriptive and historical outline, compiled for use of the New Zealand Antarctic Research Expedition Balleny Islands Reconnaissance Party 1963-1964. Antarctic Div., New Zealand, D.S.I.R. Welhngton, New Zealand, pp 1-42 Radke L (1982) Sulphur and sulphate from Mr. Erebus. Nature 299 710-712... 

SOEDER c J (1986) An Historical Outline of Applied Algology. Boca Raton, FL CRC Press. 

The true nature of electrolytic processes in electrochemistry took many years to be understood. An historical outline of the development of these ideas from the pre-Faraday period until the present time is given. One of the matters of outstanding importance for chemistry and electrochemistry was the eventual realization that electricity itself is "atomic in nature, with the electron as the natural unit of electric charge. Not until this concept was established experimentally, and understood in its theoretical ramifications, was it possible for the microscopic basis of electrolytic processes to be established, and developed more quantitatively with the correct qualitative basis. The final and correct perception of the nature of these processes provided one of the important bases for recognition of the electrical nature of matter itself and the foundations of physical chemistry. 

In this paper, an historical outline is given of the principal developments in electrochemistry concerning the mechanism and phenomen-ology of charge transfer in electrolytic processes. In tracing early contributions in this topic, it will be necessary to examine first the historical evolution of ideas about electricity and electric charge. 

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