Atomic theory and structure

DEVELOPMENT AND CENTRAL CONCEPTS OF ATOMIC THEORY AND STRUCTURE, INCLUDING THE QUANTUM MECHANICAL MODEL. 

Early Atomic Theory and Structure 81 17 Oxidation-Reduction 411... 

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... 

The theory as presented so far is clearly incomplete. The topology of the density, while recovering the concepts of atoms, bonds and structure, gives no indication of the localized bonded and non-bonded pairs of electrons of the Lewis model of structure and reactivity, a model secondary in importance only to the atomic model. The Lewis model is concerned with the pairing of electrons, information contained in the electron pair density and not in the density itself. Remarkably enough however, the essential information about the spatial pairing of electrons is contained in the Laplacian of the electron density, the sum of the three second derivatives of the density at each point in space, the quantity V2p(r) [44]. 

X-Ray absorption data in combination with atomic theory and solid-state band-structure theory can yield detailed information about the ground-state electronic structure of solids on an energy scale on the order of meV. This holds particularly true for correlated narrow-band systems, such as the rare-earth and transition-metal compounds. In broad-band materials, such as the... 

Molecular orbital theory has played the central role in the definition and understanding of problems of electronic structure. The charge density plays the corresponding role in the definition and understanding of the concepts associated with molecular structure. The previous chapters have shown that atoms, bonds, and structure are indeed consequences of the dominant topological property exhibited by a molecular charge distribution. What remains to be done is to demonstrate that the topological atom and its properties have a basis in quantum mechanics. 

Symbolic representations of atomic structure and three-dimensional representations of electron probability regions enable chemists to deal with the behavior of atoms in terms of current atomic theory and to communicate chemical information more clearly. 

Skill 20.1 Recognize the central concepts of atomic theory and atomic structure. 

ATOMIC THEORY AND THE DISCOVERY OF ATOMIC STRUCTURE (sections 2.1-2.2)... 

Gerhardt was fully convinced of his services to chemistry on his death-bed he said J ai avance la chime de cinquante ans. His outstanding contribution was his theory of types, considered later (p. 456). This emphasised the tendency, which he shared with Laurent (p. 378), to formal classification, but had a beneficial influence. His rather inflexible mentality, and his scepticism towards the atomic theory and the possibility of determining structure in the real sense, on the basis of reactions, limited his outlook and diminished to some extent the great services which he rendered to chemistry. His papers are clearer and more concise than Laurent s he usually had a better grasp of essentials and tended less to wander off into irrelevant details. 

Although atomic theory and electron configuration help us understand the arrangement and behavior of the elements, it s important to remember that the design of the periodic table is based on observing properties of the elements. Before we use the concept of atomic structure to explain how and why atoms combine to form compounds, we need to understand the characteristic properties of the elements and the trends that occur in these properties on the periodic table. These trends allow us to use the periodic table to accurately predict properties and reactions of a wide variety of substances. 

The structure of matter on a submicroscopic scale is something that has intrigued scientists for years. Modern theories of atomic structure had their origin in 1808 when John Dalton, an Englishman, published a theory based on certain facts and experimental evidence that were known at the time. Not only did he propose the existence of the atom, but he went on to precisely describe some attributes of the atom that we still hold to be true today. The listing of these attributes is called Dalton s Atomic Theory and consists of the following ... 

Bohr Niels Henrik David (1885-1962) Danish phys., known for Bohr s model of atomic structure, spectroscopic data to explain internal structure, electrons in the outer-most shall determine chem. properties ( Atomic Theory and the Description ofNature 1934)... 

It is the purpose of this section to show that the topology of the electron density p(r) yields a faithful mapping of the concepts of the molecular structure hypothesis, the concepts of atoms, bonds, and structure, a mapping that in addition provides the basis for a theory of structural stability. ... 

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