Scandium chemical properties

The chemical properties of yttrium are more similar to those of rare earths than to scandium. However, unlike the rare earths, yttrium exhibits only one valence state, -i-3. 

The first blank was filled in 1875. A French chemist discovered an element—gallium—that had all the properties Mendeleyev predicted for the space below aluminum. In 1879, a Swedish researcher discovered scandium, which looked and acted exactly how Mendeleyev said it would in its place below boron. In 1886, a German scientist discovered germanium, the element below silicon. Its chemical properties were almost exactly what Mendeleyev had predicted. 

Crystal field theory is one of several chemical bonding models and one that is applicable solely to the transition metal and lanthanide elements. The theory, which utilizes thermodynamic data obtained from absorption bands in the visible and near-infrared regions of the electromagnetic spectrum, has met with widespread applications and successful interpretations of diverse physical and chemical properties of elements of the first transition series. These elements comprise scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel and copper. The position of the first transition series in the periodic table is shown in fig. 1.1. Transition elements constitute almost forty weight per cent, or eighteen atom per cent, of the Earth (Appendix 1) and occur in most minerals in the Crust, Mantle and Core. As a result, there are many aspects of transition metal geochemistry that are amenable to interpretation by crystal field theory. 

The elements after the rare gas argon all have an inner group of electrons called the argon core and, in addition, outer electrons that determine the chemical properties of the elements. After both the 4s and 3d subsheiis are filled at zinc, the next electron goes into the 4p subshell. The elements from scandium to nickel having incomplete inner (3d) subshells comprise the first row of transition elements. The "discontinuities in the order of... 

The elements with atomic numbers from 57 (l thanum) to 71 (lutetium) are referred to as the lanthanide elements. These elements and two others, scandium and yttrium, exhibit chemical and physical properties very similar to lanthanum. They are known as the rare earth elements or rare earths (RE). Such similarity of the RE elements is due to the configuration of their outer electron shells. It is well known that the chemical and physical properties of an element depend primarily on the structure of its outermost electron shells. For RE elements with increasing atomic number, the first electron orbit beyond the closed [Xe] shell (65 remains essentially in place while electrons are added to the inner 4f orbital. Such disposition of electrons about the nucleus of the rare earth atoms is responsible for the small effect an atomic number increase from 57 to 71 has on the physical and chemical properties of the rare earths. Their assignment to the 4f orbital leads to slow contraction of rare earth size with increasing atomic number. The 4f orbitals of both europium and gadolinium are half occupied [Xe] (4F6s and [Xe] (4F5d 6s, so that there... 

The chemical properties of the transition elements do not change so strikingly with change in atomic number as do those of the other elements. In the series potassium, calcium, scandium the normal salts of the elements correspond to the maximuni oxidation numbers given by the positions of the elements in the periodic system, 1 for potas Slum, 2 for calcium, and 3 for scandium the sulfates, for example, of these elements are KoSO, CaSOj, and The fourth element,... 

Let s begin by surveying some of the key physical and chemical properties of the transition-metal elements and interpreting trends in those properties using the quantum theory of atomic structure developed in Chapter 5. We focus initially on the fourth-period elements, also called the first transition series (those from scandium through zinc in which the 3d shell is progressively filled). Then we discuss the periodic trends in the melting points and atomic radii of the second and third transition series elements. 

Scandium (Sc, at. mass 44.96) occurs in its compounds exclusively in the III oxidation state. Some of its chemical properties resemble those of the lanthanides and yttrium. Scandium hydroxide Sc(OH>3 precipitates at a pH as low as 4.8 and dissolves in alkaline medium in this respect scandium resembles aluminium. 

If we consider the vertical columns instead of the horizontal rows, we find elements with similar chemical properties listed one below the other. Group I, for example, includes hydrogen and the alkali metals like lithium and sodium. Group III includes scandium, yttrium and all the lanthanide and actinide elements. 

The elements scandium and yttrium, which are also considered to belong to the rare earth elements (because of their similar chemical behaviour) also have a 3+ oxidation state. The atomic stmcture of the REE is further discussed in Chap. 3 (Physical and Chemical Properties of the Rare Earths). 

Analyze and Plan We are asked about one physical property of scandium oxide—its state at room temperature and one chemical property—how it reacts with nitric add. 

In fact, the classification of chemical elements is valuable only in so far as it illustrates chemical behaviour, and it is conventional to use the term transition elements in a mote restricted sense. The elements in the irmer transition series from cerium (58) to lutetium (71) are called the lanthanoids those in the series from thorium (90) to lawrencium (103) are the actl-noids. These two series together make up the /block in the periodic table. It is also common to include scandium, yttrium, and lanthanum with the lanthanoids (because of chemical similarity) and to include actinium with the actinoids. Of the remaining transition elements, it is usual to speak of three main transition series from titanium to copper from zirconium to silver and from hafnium to gold. All these elements have similar chemical properties that result from the presence of unfilled d-orbltals in the element or (in the case of copper, silver, and gold) in the ions. The elements from 104 to 109 and the undiscovered elements 110 and 111 make up a fourth transition series. The elements zinc, cadmium, and mercury have filled d-orbltals both in the elements and in compounds, and are usually regarded as nontransition elements forming group 12 of the periodic table. 

Scandium Thermodynamic Properties, Chemical Equilibria, and Standard Potentials... 

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. 

They have very close chemical properties with scandium and yttrium and the whole series is often referred as rare earth elements, since lanthanides were historically isolated from uncommon oxide-type minerals. However this term is not totally adequate, the lanthanides are not to be considered as rare, because even a scarce 4f-element such as lutetium is more abundant than silver (see Geology, Geochemistry, and Natural Abundances of the Rare Earth Elements). 

The rare earth elements (REE) include lanthanum and the f-block elements, cerium through lutetium. Scandium and yttrium are included in this group as they have ionic radii similar to the lighter f-block elements and are found together in the same ores. The chemical similarities of the 17 REE make diem unique in comparison to the other metals in the periodic table where two adjacent elements in a period typically have significantly different chemical properties. This makes the REE relatively difficult to separate from one another, although there are minerals where the lighter (La Eu) and heavier (Y and Gd Lu) REE are concentrated. REE research has benefited from this similarity, however, as compounds and materials formed with one REE can often be replicated with one or more of the other REE. 

Trends in atomic radii are of concern because chemical properties are determined in part by atomic size. Looking at the fourth-period covalent radii (one measure of atomic size) in Table 23.1, you see that they decrease quickly from scandium (144 pm) to titanium (132 pm) and vanadium (122 pm). This decrease in atomic size across a row is also observed in the main-group elements. It is due to an increase in effective nuclear charge that acts on the outer electrons and pulls them in more strongly. The effective nuclear charge is the positive charge Telf by an electron it equals the nuclear charge minus the... 

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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