Periodic Classification

It is an interesting speculation as to how much more difficult the isolation of these two elements might have been if the periodic classification had not provided us with a very good preview of their chemistries. 

The elements of Group O of the Periodic Classification are rare and inert. Criticise this statement, giving evidence in support of your criticisms. 

Before it was known that elements beyond uranium were capable of existence, the heaviest known natural elements, thorium, protactinium and uranium, were placed in a sixth period of the periodic classification, corresponding to the elements hafnium, tantalum and tungsten in the preceding period. It was therefore implied that these elements were the beginning of a new, fourth transition series, with filling of the penultimate n = 6 level (just as the penultimate = 5... 

The isolation and identification of 4 radioactive elements in minute amounts took place at the turn of the century, and in each case the insight provided by the periodic classification into the predicted chemical properties of these elements proved invaluable. Marie Curie identified polonium in 1898 and, later in the same year working with Pierre Curie, isolated radium. Actinium followed in 1899 (A. Debierne) and the heaviest noble gas, radon, in 1900 (F. E. Dorn). Details will be found in later chapters which also recount the discoveries made in the present century of protactinium (O. Hahn and Lise Meitner, 1917), hafnium (D. Coster and G. von Hevesey, 1923), rhenium (W. Noddack, Ida Tacke and O. Berg, 1925), technetium (C. Perrier and E. Segre, 1937), francium (Marguerite Percy, 1939) and promethium (J. A. Marinsky, L. E. Glendenin and C. D. Coryell, 1945). 

The alkali metals form a homogeneous group of extremely reactive elements which illustrate well the similarities and trends to be expected from the periodic classification, as discussed in Chapter 2. Their physical and chemical properties are readily interpreted in terms of their simple electronic configuration, ns, and for this reason they have been extensively studied by the full range of experimental and theoretical techniques. Compounds of sodium and potassium have been known from ancient times and both elements are essential for animal life. They are also major items of trade, commerce and chemical industry. Lithium was first recognized as a separate element at the beginning of the nineteenth eentury but did not assume major industrial importance until about 40 y ago. Rubidium and caesium are of considerable academic interest but so far have few industrial applications. Francium, the elusive element 87, has only fleeting existence in nature due to its very short radioactive half-life, and this delayed its discovery until 1939. 

In its chemistry, silicon is clearly a member of Group 14 of the periodic classification but there are notable differences from carbon, on the one hand, and the heavier metals of the group on the other (p. 371). Perhaps the most... 

If argon be a single element then there is reason to doubt whether the periodic classification of elements is complete whether in fact elements may not exist that cannot be fitted among those of which it is composed. (Rayleigh and Ramsay, 1895, p. 58)... 

Some indication of the differences can be found by analysing some criticisms. .. upon the periodic classification solicited in 1881 by the editor of the Chemical News from Adolphe Wurtz, a celebrated Parisian chemist of the time. (Wurtz s note follows notes from Mendeleev and from Lothar Meyer forming their famous priority dispute.)... 

The aim of the present article is to elevate the role of triads to an even greater extent. Since triads are now expressed in terms of atomic numbers they coincidentally characterize the elements as basic substances. In other words they characterize the true basis for periodic classification compared with the elements as simple substances, as argued by Mendeleev and more recently by Paneth and other authors. 

The existence of this element was predicted by Mendeleev as a missing link between aluminum and indium during his periodic classification of elements. Mendeleev termed it ekaaluminum. The element was discovered in 1875 by French chemist Lecoq de Boisbaudran while he was carrying out spectroscopic examination of emission lines from Pyrenean zinc blende concentrates. Boisbaudran named this new element gallium, after Gallia, the Latin word for his native France. In the same year, Boisbaudran also separated gaUium by electrolysis. 

The Electronic Configurations of Atoms the Periodic Classification of the Elements... 

The chemistry of an element is determined by the manner in which its electrons are arranged in the atom. Such arrangements are the basis of the modern periodic classification of the elements the Periodic Table. 

The treatment of atoms with more than one electron (polyelectronic atoms) requires consideration of the effects of interelectronic repulsion, orbital penetration towards the nucleus, nuclear shielding, and an extra quantum number (the spin quantum number) which specifies the intrinsic energy of the electron in any orbital. The restriction on numbers of atomic orbitals and the number of electrons that they can contain leads to a discussion of the Pauli exclusion principle, Hund s rules and the aufbau principle. All these considerations are necessary to allow the construction of the modern form of the periodic classification of the elements. 

The trends in first ionization energies, first electron attachment energies, atomic sizes and electronegativity coefficients of the elements across the groups and down the periods of the periodic classification. 

Some method of classifying the elements for treatment in this way is clearly essential, and we have adopted the Periodic Classification with slight alterations, devoting a whole volume to the consideration of the elements in each vertical column, as will be evident from a glance at the scheme in the Frontispiece. 

Hydrogen and the ammonium salts are dealt with in Volume II, along with the Elements of Group I. The position of the rare earth metals in the Periodic Classification has for many years been a source of difficulty. They have all been included in Volume IV, along with the Elements of Group III, as this was found to be the most suitable place for them. 

Caplan, Paula J. Pathologizing Your Period Classification of Premenstrual Syndrome in Diagnostic and Statistical Manual of Mental Disorders. Ms. 18, no. 3 (Summer 2008) 63-64. Feminists criticize psychiatrists for... 

Figure 14.16—Elements determined by AAS or FES. Most elements can be determined by atomic-absorption or flame emission using one of the available atomisation modes (burner, graphite furnace or hydride formation). Sensitivity varies enormously from one element to another. The representation above shows the elements in their periodic classification in order to show the wide use of these methods. Some of the lighter elements, C, N, O, F, etc. in the figure can be determined using a high temperature thermal source a plasma torch, in association with a spcctropholometric device (ICP-AbS) or a mass spectrometer (1CP-MS).

Periodic classifications oTthe dements by Dmitri Mendeleev and by LotharMcycrappciired m 1869 For a centennial-cdebraiing discission of the periodic table, see van Spronsen. J. W. The Periodic System of Chemical Elements Elsevier Amsterdam. 1969. 

The elements vanadium, niobium, tantalum and protoactinium constitute Subdivision A of the Fifth Group of the Periodic Classification. The general properties of Subdivision B are considered elsewhere in... 

ALKALINE EARTHS. The elements of group 2 of the periodic classification. In order of increasing atomic number, they are beryllium,... 

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