Scandium general properties

It was not until 1859 that Bunsen first applied the spectrograph to analytical chemistry determinations, and this development proved useful in the case of the rare earths. The nature of the spectra of the various rare earths was not understood until well into the Twentieth century, so the analytical methods were empirical and not always dependable. The uncertainty was due to the fact that the transition elements also separated along with the rare earths in the fractionation process, and tended to complicate the various spectra obtained. As a result of these complications, the discovery of over 70 new rare earths was reported in the literature. Many of the new elements were based on spectra differences in the fractions obtained, and no one knew how many rare earths should exist. It was not until 1869 that Mendeleyev published his first periodic chart. Incidentally, in doing so, he had to leave a blank where scandium now occurs, and he predicted a new element would be found which would have the general properties now attributed to the rare earths. Shortly afterwards (1879) scandium was discovered, and its discovery greatly aided in the general acceptance of Mendeleyev s ideas. While the chart had a place for lanthanum, there was no place in his chart for the other rare earths, since they also seemed to fall in the space reserved for lanthanum. The early chemists seemed to think they were discovering a new type of element with properties very similar to the properties which we now ascribe to isotopes, and some even speculated that these other rare earths were different modifications of lanthanum. 

Table 1. General properties of ions of scandium, yttrium, lanthanum and lanthanoids. 

The second group is characterized by a smaller number of ternary compounds, which may be explained by the similarity of the crystallochemical behaviours of the two components Be, Mg, Ga or Ge, and Al. As one can see, scandium generally forms a small number of compounds in the investigated systems (Sc is rather similar with a 3d transition metal, than with the other rare earths). All of the ternary compounds with solved crystal structures are characterized by structure types of the binary compounds or closely related ones. Systems with Ge and Al show the La202S type of crystal structure. This may be explained by the partially semimetallic properties of Al in these systems. 

General Properties 23-2 Principles of Extractive Metallurgy 23-3 Metallurgy of Iron and Steel 23-4 First-Row Transition Elements Scandium to Manganese 23-5 The Iron Triad Iron, Cobalt, and Nickel... 

The person whose name is most closely associated with the periodic table is Dmitri Mendeleev (1836-1907), a Russian chemist. In writing a textbook of general chemistry, Mendeleev devoted separate chapters to families of elements with similar properties, including the alkali metals, the alkaline earth metals, and the halogens. Reflecting on the properties of these and other elements, he proposed in 1869 a primitive version of today s periodic table. Mendeleev shrewdly left empty spaces in his table for new elements yet to be discovered. Indeed, he predicted detailed properties for three such elements (scandium, gallium, and germanium). By 1886 all of these elements had been discovered and found to have properties very similar to those he had predicted. 

Scandium, yttrium, and the lanthanide mettils comprise 17 elements for which systematically-determined mechanical property data are sparse. Pioneering work on the mechanical properties of rare earth metals was done in the mid to late 1950 s and was conducted almost exclusively by three groups B. Love and associates at Research Chemicals, Inc. C.R. Simmons and associates at General Electric Co. and E.M. Savitskiy and associates in the USSR. Since that time the number of investigations has increased and the property values have changed considerably with improvements in metal purification methods. 

Simmons, C.R., 1959, The Mechanical Properties of Yttrium, Scandium and the Rare Earth Metals, AECU-4423, General Electric Co., Aircraft Nuclear Propulsion Dept., Cincinnati, Ohio. 

Rare-earth elements, in contrast to their historical name, are relatively abundant in the Earth s crust, and they occur in many economically viable ore deposits throughout the world with estimated worldwide reserves of 110 million tonnes. For instance, cerium (Ce), which is the most abundant rare earth, has a relative abundance of 66.5 mg/kg, similar to that of zinc, while thuhum (Tm), which is the least abundant, has a relative abundance of 0.52 mg/kg, greater than that of cadmium and silver. The abundance of lanthanides in nature shows an even-odd alteration with atomic number. As a general rule, owing to their extremely similar chemical properties, especially valences and ionic radii, geochemical processes often concentrate these elements in the same minerals, where elements are intimately mixed, and therefore they always occur in the same ore deposits. Nevertheless, owing to its smaller atomic and ionic size, scandium only occurs in rare-earth ores in minor amounts. 

In general, the ionic radii give an indication of the expected coordination number in a rare earth complex, though this is more apparent in aqueous solutions than in the solid state, where bulky ligands and different coordination modes may result in unexpected CNs. Scandium with its smaller ionic size has a significantly lower average coordination number than the other rare earths. The properties of scandium and yttrium, which are partly due to the ionic radii, are discussed in relation to those of the lanthanides in section 1.3.4. 

The connection between the phenomenological shell model (PSM) and aromaticity of metal clusters is presented in this chapter. This model allows us to probe the aromaticity of metal clusters, and also organic compounds, in a general framework and context. The 4n + 2 rule of planar rings is shown to be a special case of this model. It can be applied to the cases of planar, spherical, and distorted (oblate and prolate) clusters. The different criteria (stability, symmetry, magnetic properties, electronic structure) are considered with the examples of different scandium-doped copper clusters Cu c and Cu c+. In summary, a closed electronic structure according to the PSM often results in an aromatic behavior. 

While the lanthanide series is due to the successive filling of the 4f orbitals, it is generally assumed that they do not contribute significantly to bonding due to their limited radial extension and the shielding from the valence shell by the filled 5s and 5p orbitals. However, these f-orbitals (filled or empty) should be able to modulate some electronic properties of the metal center. In the ubiquitous oxidation state 3+, the lanthanide ions reach an inert gas core configuration by the loss of one 4f electron. It is for this reason that yttrium and scandium complexes are included in discussions of lanthanide chemistry i.e., in their predominant 3+ oxidation states, these elements have an inert gas core configuration ([Kr] and [Ar], respectively) and empty d orbitals. Indeed, due to the lanthanide contraction, the size of Y + falls between Ho and Er +, whereas scandium is considerably smaller than the lanthanides. 

Rare eartb metals (REM), wbicb include tbe 15 lantbanoids as well as yttrium and scandium, tend to occur in tbe same ore deposits and exhibit similar chemical properties. The term rare earth is misleading because it implies scarcity and high costs as impediments for the use of these metals. Indeed, the element concentrations in the continental crust (Figure 6.1) show that even the rarest lanthanoid thulium is far more common than some precious metals, e.g. silver and gold, and the most abundant lanthanoid cerium is even more common than copper. However, because of their geochemical properties, rare earth elements have very little tendency to become concentrated in exploitable ore deposits. Consequently, most of the world s supply of REM comes from only a handful of sources. It was the very scarcity of these minerals (previously called "earths") that led to the term "rare earth". The REM are also considered as non-toxic and generally not expensive. 

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