Elements atomic structure

Group 13 (IIIA) perchlorates, 28 278 Group 13 (IIIB) peroxides, 28 398 401 Group 14 (IV) elements, atomic structure of, 22 232-233... 

As explained in the entry on Chemical Elements Atomic Structure of... 

Fundamentals of chemistry—atoms, elements, atomic structure, hydrocarbons, states of matter, gases, solutions... 

We should keep these facts in mind as we examine the effects of quantum theory on chemistry in the twentieth century. The original investigators of quantum theory were well aware that the new theory should open the black box of elemental atomic structure but while physicists could initially be content with a theory that would differentiate the various elements, chemists needed one that could accoimt for the patterns they had discerned. In other words, the chemist looked to the quantum theory to provide some explanation of the patterns and sets captmed in the periodic table. 

A representation of atomic structure. The various spheres are not drawn to scale. The lump of iron on the left would contain almost a million million million million (10 ) atoms, one of which is represented by the sphere in the top center of the page. In turn, each atom is composed of a number of electrons, protons, and neutrons. For example, an atom of the element iron contains 26 electrons, 26 protons, and 30 neutrons. The physical size of the atom is determined mainly by the number of electrons, but almost all of its mass is determined by the number of protons and neutrons in its dense core or nucleus (lower part of figure). The electrons are spread out around the nucleus, and their number determines atomic size but the protons and neutrons compose a very dense, small core, and their number determines atomic mass. 

With only 90 elements, one might assume that there could be only about 90 different substances possible, but everyday experience shows that there are millions of different substances, such as water, brick, wood, plastics, etc. Indeed, elements can combine with each other, and the complexity of these possible combinations gives rise to the myriad substances found naturally or produced artificially. These combinations of elemental atoms are called compounds. Since atoms of an element can combine with themselves or with those of other elements to form molecules, there is a wide diversity of possible combinations to make all of the known substances, naturally or synthetically. Therefore, atoms are the simplest chemical building blocks. However, to understand atoms, it is necessary to examine the structure of a typical atom or, in other words, to examine the building blocks of the atoms themselves. The building blocks of atoms are called electrons, protons, and neutrons (Figure 46.1). 

Str-ucture determines properties and the properties of atoms depend on atomic structure. All of an element s protons are in its nucleus, but the element s electrons are distributed among orbitals of var ying energy and distance from the nucleus. More than anything else, we look at its electron configuration when we wish to understand how an element behaves. The next section illustrates this with a brief review of ionic bonding. 

There is no single best form of the periodic table since the choice depends on the purpose for which the table is used. Some forms emphasize chemical relations and valence, whereas others stress the electronic configuration of the elements or the dependence of the periods on the shells and subshells of the atomic structure. The most convenient form for our purpose is the so-called long form with separate panels for the lanthanide and actinide elements (see inside front cover). There has been a lively debate during the past decade as to the best numbering system to be used for the individual... 

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... 

Given the efficiency of VASP, electronic structure calculations with or without a static optimization of the atomic structure can now be performed on fast workstations for systems with a few hundred inequivalent atoms per cell (including transition-metais and first row elements). Molecular dynamics simulationsextending over several picoseconds are feasible (at tolerable computational effort) for systems with 1000 or more valence electrons. As an example we refer to the recent work on the metal/nonmetal transition in expanded fluid mercury[31]. 

To understand how the electron has been applied to explanations of the periodic table we must start with the discovery of the periodic system itself. The Russian chemist Dimitri Mendeleev announced in 1869 that the properties of elements arranged in order of increasing atomic weight appeared to repeat after certain definite intervals. Yet even as this discovery became increasingly well established, Mendeleev remained strongly opposed to any attempt to reduce or explain the periodicity in terms of atomic structure. He resisted the notion of any form of primary matter, which was actively discussed by his contemporaries, and opposed... 

Moseley photographed characteristic spectra for some 38 elements that could serve as x-ray tube targets. In two papers,37 he not only uncovered structure in the K and L spectra—he alscr established the atomic number as more fundamental than the atomic weight, and he provided brilliant support for- the Bohr theory of atomic structure. 

This chapter builds an understanding of atomic structure in four steps. First, we review the experiments that led to our current nuclear model of the atom and see how spectroscopy reveals information about the arrangement of electrons around the nucleus. Then we describe the experiments that led to the replacement of classical mechanics by quantum mechanics, introduce some of its central features, and illustrate them by considering a very simple system. Next, we apply those ideas to the simplest atom of all, the hydrogen atom. Finally, we extend these concepts to the atoms of all the elements of the periodic table and see the origin of the periodicity of the elements. 

What Do We Need to Know Already The information in this chapter is organized around the principles of atomic structure and specifically the periodic table (Chapter 1). However, the chapter draws on all the preceding chapters, because it uses those principles to account for the properties of the elements. 

The materials for solid solutions of transition elements in j3-rh boron are prepared by arc melting the component elements or by solid-state diffusion of the metal into /3-rhombohedral (/3-rh) boron. Compositions as determined by erystal structure and electron microprobe analyses together with the unit cell dimensions are given in Table 1. The volume of the unit cell (V ) increases when the solid solution is formed. As illustrated in Fig. 1, V increases nearly linearly with metal content for the solid solution of Cu in /3-rh boron. In addition to the elements listed in Table 1, the expansion of the unit cell exceeds 7.0 X 10 pm for saturated solid solutions " of Ti, V, (2o, Ni, As, Se and Hf in /3-rh boron, whereas the increase is smaller for the remaining elements. The solubility of these elements does not exceed a few tenths at %. The microhardness of the solid solution increases with V . Boron is a brittle material, indicating the accommodation of transition-element atoms in the -rh boron structure is associated with an increase in the cohesion energy of the solid. 

We show in Chapter 2 that the periodic table is based on the structure of atoms rather than on their masses. Elemental masses correlate closely with atomic structure, however, so ordering by mass is almost the same as ordering by structure. There are... 

Each element has a unique emission pattern that provides valuable clues about atomic structure. 

Silicon s atomic structure makes it an extremely important semiconductor. Highly purified silicon, doped with such elements as boron, phosphorus, and arsenic, is the basic material used in computer chips, transistors, sUicon diodes, and various other electronic circuits and electrical-current switching devices. Silicon of lesser purity is used in metallurgy as a reducing agent and as an alloying element in steel, brass, and bronze. 

In this chapter, only atomic spectrochemical methods are discussed. Atomic spectra are line spectra, and are specific to the absorbing or emitting atoms (elements), i.e. the spectra contain information on the atomic structure. Each spectral line can be regarded as the difference between two atomic states ... 

Krebs, Robert E. The history and use of our earth s chemical elements a reference guide. Westport (CT) Greenwood P, 1998. ix, 346p. ISBN 0-313-30123-9 A short history of chemistry — Atomic structure The periodic table of the chemical elements — Alkali metals and alkali earth metals - Transition elements metals to nonmetals — Metallics and metalloids - Metalloids and nonmetals — Halogens and noble gases - Lanthanide series (rare-earth elements) — Actinide, transuranic, and transactinide series... 

A predominant feature of the atomic structure of the lanthanide group is the sequential addition of 14 electrons to the 4f subshell (Table 1). The /"electrons do not participate in bond formation and in ordinary aqueous solutions all of the lanthanides exhibit a principal (III) state. The common (III) state confers a similarity in chemical properties to all lanthanide elements. Some of the lanthanides can also exist in the (II) state (Nd, Sm, Eu, Tm, Yh) or in the (IV) state (Ce, Pr, Nd, Tb, Dy). Except for Ce(IV), Eu(II), and Yb(II), these unusual lanthanide oxidation states can only be prepared under drastic redox pressure and temperature conditions, and they are not stable in aqueous solutions. Cerium (IV) is a strong oxidizing agent... 

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