Transition elements elemental substances

The Niccolite Structure. The substances which crystallize with the niccolite structure (B8) are compounds of transition elements with S, Se, Te, As, Sb, Bi, or Sn. The physical properties of the substances indicate that the crystals are not ionic, and this is substantiated by the lack of agreement with the structural rules for ionic crystals. Thus each metal atom is surrounded by an octahedron of non-metal atoms but these octahedra share faces, and the edges of the shared faces are longer than other edges (rather than shorter, as in ionic crystals). Hence we conclude that the bonds are covalent, with probably some metallic character also. 

Lanthanides form soluble complexes with many inorganic and organic substances however, the nature of the bonding in these complexes has not been completely determined. There is evidence for either ionic or covalent bond formation or a combination of both. Lanthanides are complexed by inorganic ions, but not as readily as are the transition elements. The inorganic complexes are not as important... 

The reliable experimental information on the absolute scale and thermal vibrations of beryllium metal made it possible to analyze the effect of the model on the least-squares scale factor, and test for a possible expansion of the 1 s core electron shell. The 0.03 A y-ray structure factors were found to be 0.7% lower than the LH data, when the scale factor from a high-order refinement (sin 6/X) > 0.65 A l) is applied. Larsen and Hansen (1984) conclude that because of the delocalization of the valence electrons, it is doubtful that diffraction data from a metallic substance can be determined reliably by high-order refinement, even with very high sin 0/X cut-off values. This conclusion, while valid for the lighter main-group metals, may not fully apply to metals of the transition elements, which have much heavier cores and show more directional bonding. 

D-Block Element a transition element, valence electrons are in the d orbitals Decay Activity the rate of decay of a radioactive substance... 

Xia, K., Bleam, W., and Helmke, P. A. (19976). Studies of the nature of binding sites of first row transition elements bound to aquatic and soil humic substances using X-ray absorption spectroscopy. Geochim. Cosmochim. Acta 61, 2223-35. 

Lewis hi his It tG paper and in his book on valence emphasized the fact that there exist only a few stable molecules and complex ions (other than those containing atoms of the transition elements) for which the total number of electrons is odd. He pointed out that in general an odd molecule, such as nitric oxide or nitrogen dioxide, would be expected to use its unpaired electron to form a bond with another such molecule, and that the monomeric substance should accordingly be very much less stable than its dimer and he stated that the method by winch the unpaired electron is firmly held in the stable odd molecule v/as not at that time understood. Since then the explanation of the phenomenon has been found, as the result of the... 

In the unusually effective reducing medium of sodium-hexamethylphos-phoramide (HMPA), [Mn(CO)5] underwent facile reduction to form a golden yellow to yellow brown solution. On the basis mainly of derivative chemistry and infrared spectra, the major soluble component was formulated as Na3[Mn(CO)4] (14). Once this materia] was in hand it was evident that similar binary carbonyl trianions should be possible for other rf-block transition elements of odd atomic number. Since 1976, syntheses of mononuclear binary carbonyl trianions of V, Nb, Ta, Re, Co, Rh, and Ir have also been reported from this laboratory (vide infra). Because these substances contain transition metals in their lowest known oxidation states, they have often been referred to as superreduced species (15). 

Soft metallic elements such as Al, In, Pb, Hg, Sn, Zn, Tl, Ga, Cd, V and Nb are type I superconductors. Alloys and chemical compounds such as Nb3Sn, V3Ga, and lZa3In, and some transition elements, are type II superconductors. Type II substances generally have a higher Tc than do type I superconductors. The recently discovered transition metal oxide superconductors have generated intense interest because they are type II superconductors with very high transition temperatures. Table 13.1 summarizes Tc for selected superconductors. 

Consider a substance where the unpaired electrons are deemed to reside in d orbitals, localised - as in CF theory - upon ions of a transition element, n on each centre. The total spin 5 of each ion is equal to nil. If a... 

The ionic model is of limited applicability for the heavier transition series (4d and 5d). Halides and oxides in the lower oxidation states tend to disproportionate, chiefly because of the very high atomisation enthalpies of the elemental substances. Many of the lower halides turn out to be cluster compounds, containing metal-metal bonds (see Section 8.5). However, the ionic model does help to rationalise the tendency for high oxidation states to dominate in the 4d and 5d series. As an example, we look at the fluorides MF3 and MF4 of the triad Ti, Zr and Hf. As might be expected, the reaction between fluorine gas and the elemental substances leads to the formation of the tetrafluorides MF4. We now investigate the stabilities of the trifluorides MF3 with respect to the disproportionation ... 

Most Phase I oxidations are performed by cytochrome P-450. "Cytochrome," derived from Greek, literally means "colored substance in the cell." The color is derived from the properties of the outer electrons of the transition element iron. "P-450" denotes a reddish pigment with the unusual property of having its major optical absorption peak (Soret maximum) at about 450 nm, when it has been reduced and combined with carbon monoxide.330 Although the name "P-450" was intended to be temporary (until more was known about the substance), the terminology has persisted for 18 yr because of the increasing complexity of this enzyme system and because of the lack of agreement on new nomenclature. 

In the field of not only traditional metallurgy but also recently developed nano-technology, it is very interesting and important what change is introduced when it is surrounded by other atoms. Such a change in electronic states has been investigated as chemical shift detected by X-ray (XPS) and UV (UPS) photoemission spectroscopy [1] as well as X-ray emission and absorption spectroscopy [2,3]. Also, such a chemical shift has been simulated by theoretical calculation [4]. However, many problems have been unsolved. In the case of XPS and UPS, since the most outer layers of substances are analyzed, the spectra are easily affected by absorbed gaseous molecules. Also, with the X-ray emission and absorption spectroscopy it is difficult to analyze the complicated X-ray transition states for substances composed of heavy metal elements. Therefore, a complementary method has been demanded for the spectroscopy such as XPS, UPS and X-ray emission and absorption spectroscopy. The coefficient y of the electronic contribution to heat capacity, Cp, near absolute zero Kelvin reflects the density of states (DOS) in the vicinity of Fermi level (EF) [5]. Therefore, the measurement of y is expected to be one of the useful methods to clarify the electronic states of substances composed of heavy metal elements. 

The essential condition for ferromagnetic behaviour is the presence of magnetic dipoles in a substance. This is set by atomic structure. At least one of the ferrite cations must have one or more unpaired electrons. The spinning unpaired electron will impart to the ion a magnetic moment. This condition is complied with in the group of transition elements (Mn, Fe, Co, Ni, Cu, etc.). 

The group B elements, or transition elements, are divided into transition metals and inner transition metals. The two sets of inner transition metals, known as the lanthanide and actinide series, are located along the bottom of the periodic table. The rest of the group B elements make up the transition metals. Elements from the lanthanide series are used extensively as phosphors, substances that emit light when struck by electrons. The How It Works at the end of the chapter explains more about phosphors and how images are formed on a television screen. 

The transition metals tend to form positive ions by losing electrons, just like the representative metals. Metals, whether representative or transition, share this characteristic. However, the transition elements are characterized as "variable valence" elements depending on the type of substance with which they react, they may form more than one stable ion. For example, iron has two stable ionic forms ... 

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