Classification of metals

They indicated that the softness parameter may reasonably be considered as a quantitative measure of the softness of metal ions and is consistent with the HSAB principle by Pearson (1963, 1968). Wood et al. (1987) have shown experimentally that the relative solubilities of the metals in H20-NaCl-C02 solutions from 200°C to 350°C are consistent with the HSAB principle in chloride-poor solutions, the soft ions Au" " and Ag+ prefer to combine with the soft bisulfide ligand the borderline ions Fe +, Zn +, Pb +, Sb + and Bi- + prefer water, hydroxyl, carbonate or bicarbonate ligands, and the extremely hard Mo + bonds only to the hard anions OH and. Tables 1.23 and 1.24 show the classification of metals and ligands according to the HSAB principle of Ahrland et al. (1958), Pearson (1963, 1968) (Table 1.23) and softness parameter of Yamada and Tanaka (1975) (Table 1.24). Compari.son of Table 1.22 with Tables 1.23 and 1.24 makes it evident that the metals associated with the gold-silver deposits have a relatively soft character, whereas those associated with the base-metal deposits have a relatively hard (or borderline) character. For example, metals that tend to form hard acids (Mn +, Ga +, In- +, Fe +, Sn " ", MoO +, WO " ", CO2) and borderline acids (Fe +, Zn +, Pb +, Sb +) are enriched in the base-metal deposits, whereas metals that tend to form soft acids... 

Classification of metals and ligands according to the HSAB principle... 

Present understanding of Lewis acidity and basicity is based mainly on the A and B type classification of metal ions of Ahrland, Chatt,... 

This is the most common route, the reagent being a metal compound/solvent combination. Typical conditions call for the metal salt (e.g., acetate) in a buffer system (e.g., NaOAc/AcOH) and a co-solvent such as chloroform. Generally the reaction mixture is refluxed until the metal complex spectrum (see Section 9.22.5.6 and Table 4) is fully developed. Metal acetylacetonates and metal phenoxides have also been employed. The topic has been reviewed in detail by Buchler,51 who has also summarized the history and classification of metal complexes of this series, and the mechanisms of metalation.52... 

Table 16.2 Hard-Soft Classification of Metals (Lewis acids) and Ligands (Lewis bases). ...

Many observations concerning these trends had been made over the years, and in the 1950s S. Ahrland, J. J. Chatt, and M. Davies presented a classification of metals based on their preferred interaction with donor atoms. Class A metals are those that interact preferentially when the donor atom is in the first row of the periodic table. For example, they prefer to bond to N rather than P donor atoms. Class B metals are those which interact better when the donor atom is in the second row of the periodic table. For example, a class B metal would bond better to P than to N. The following table summarizes the behavior of metal atoms according to this classification. 

Table 20.1 Classification of Metal Ions on the Basis of H20 Exchange Rate. ...

Although the classification of metal-metal bonds into distinct a, n, and 5 types is reasonably clear in HW=WH (C2h), such diatomic symmetry labels may become... 

Table 1.7 Hard-Soft Acid-Base Classification of Metal Ions and Ligands...

This is an on-going project aimed at examining the T/D characteristics of metals and alloys in a marine medium in seven- and twenty eight-day tests. The data obtained to date on seven-day tests of cuprous oxide (Cu20) and nickel metal powder (Ni) provides useful comparisons with those reported earlier for the freshwater OECD 203-based media at pH 6 and 8 (Skeaff Hardy 2005) and insight into the behaviour of metal-bearing substances used in commerce under marine conditions of the T/DP. The data supports an approach directed to the eventual adaptation, validation and application of the OECD T/DP to marine systems for the purposes of marine hazard classification of metals, metal compounds and alloys. 

The remaining exceptions concern the lanthanide series, where samarium at room temperature has a particular hexagonal structure and especially the lower actinides uranium, neptunium, and plutonium. Here the departure from simple symmetry is particularly pronounced. Comparing these three elements with other metals having partly filled inner shells (transition elements and lanthanides), U, Pu, Np have the lowest symmetry at room temperature, normal pressure. This particular crystallographic character is the reason why Pearson did not succeed to fit the alpha forms of U, Pu, and Np, as well as gamma-Pu into his comprehensive classification of metallic structures and treated them as idiosyncratic structures . Recent theoretical considerations reveal that the appearance of low symmetries in the actinide series is intimately linked to the behaviour of the 5f electrons. 

Table 3. Classification of metals and semi-metals based on adsorption properties. (A indicates adsorption, NA no adsorption.) (From Ref. )...

Jhe classification of metal complex reactions as 14 labile and 11 inert by Taube (121) was based essentially on literature of qualitative observations. In the last decade or so this situation has changed dramatically, as even a cursory examination of the Tables will show. 

Nieboer, E. Richardson, D. H. S. 1980. The replacement of the nondescript term heavy metal by a biologically and chemically significant classification of metal ions. Environmental Pollution (Ser. B), 1, 3-26. 

A useful concept for the classification of metal-containing proteins has been suggested by Vallee The proteins are divided into two groups metalloproteins and metal-protein complexes, on the basis of their stability during the isolation procedures. Metalloproteins retain their metal constituent during fractionation and there is a stoichiometric relationship between the metal and protein. On the other hand, the metal is loosely bound and easily lost during dialysis in metal-proteins. Examples of both types of proteins can be found in an article by Vallee and Coleman... 

Various metal-oxides were tested as catalysts at a temperature of 550°C, since better performances had been obtained a 500 to 550°C [19-21]. The results are listed in Tables 1-3, according to the classification of metal oxide in view of both acid-base and oxidizing functions [22,23]. 

A Classification of Metal Sulfides and Their Types of Metal-Sulfur Bonds 525... 

Such a situation was clear, in principle, long ago, and in this respect various classifications of metal complexes were offered according to coordination number [18,32], oxidation state of the central ion [32], electronic configuration of the metal center [32], nature of the coordination bond [32], character of the electric charge of the coordination sphere (cationic, anionic, and neutral) [116,121,122], number of nuclei (metals) in the complexes [121-123], and dentacity of ligands [121]. However, such a division of complexes comes short of satisfying modern coordination chemistry. 

The classification of metals, their salts, and organometallic compounds, based on the Principle of Hard-Soft Acids and Bases (HSAB) of Pearson [112,116,156-158], is discussed in detail in Sec. 1.2.2. 

In addition to his work on titrimetry, Gay-Lussac made important contributions in other areas of analytical chemistry. He studied the reactions of hydrogen sulphide in different media, thus laying the foundations for the classification of metals into different analytical groups, and in conjunction with Thenard, he developed the first truly practicable method for the determination of carbon and hydrogen in organic compounds.54... 

Table 6.2 Emf series of some elements and classification of metals and metalloids in order of nobility23...

Table 10 Classification of metal ions into A and B- type and after the Pearson concept into hard and soft acids with preferred ligands (after Stumm and Morgan 1996)...

Materials of construction may be divided into the two general classifications of metals and nonmetals. Pure metals and metallic alloys are included under the first classification. Table 1 presents data showing the comparison of purchased cost for various types of metals in plate form. 

Figure 3.5. Classification of metal complexes according to their dissociation kinetics.

THE BASIC ELECTROCHEMICAL concepts and ideas underlying, the phenomena of metal dissolution are reviewed. The emphasis is on the electrochemistry of metallic corrosion in aqueous solutions. Hie role of oxidation potentials as a measure of the "driving force" is discussed and the energetic factors which determine the relative electrode potential are described. It is shown that a consideration of electrochemical kinetics, in terms of current-voltage characteristics, allows an electrochemical classification of metals and leads to the modern views of the electrochemical mechanism of corrosion and passivity. 

Both kinetic and thermodynamic classifications of metal-nitrogen complexes have been proposed. The former gives systems that are either coordinatively inert or labile see Coordinatively Inert Labile Complexes), with inert being defined as fhose that allow geometric isomers see... 

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