Metallic elements lanthanides

As a group of typical metal elements, lanthanide elements can form chemical bonds with most nonmetal elements. Some low-valence lanthanide elements can form chemical bonds in organometallic or atom cluster compounds. Because lanthanide elements lack sufficient electrons and show a strong repulsive force towards a positive charge, chemical bonds between lanthanide metals have not yet been observed. Table 1.4 shows that 1391 structure-characterized lanthanide complexes were reported in publications between 1935 and 1995 and these are sorted by chemical bond type. 

The methods listed thus far can be used for the reliable prediction of NMR chemical shifts for small organic compounds in the gas phase, which are often reasonably close to the liquid-phase results. Heavy elements, such as transition metals and lanthanides, present a much more dilficult problem. Mass defect and spin-coupling terms have been found to be significant for the description of the NMR shielding tensors for these elements. Since NMR is a nuclear effect, core potentials should not be used. 

Elements measured Two-thirds of the periodic table transition metals, halogens, lanthanides, and platinum-group metals... 

Rare earth (RE) is a generic name for 14 metallic elements of the lanthanide series. These elements have similar chemical propenies and are usually supplied as a mixture of oxides extracted from ores such as bastnaesite or monazite. 

Rare Earth is a generic name used for the 14 metallic elements of the lanthanide series used in the manufacturing of FCC catalyst to improve stability, activity, and gasoline selectivity of the zeolite. 

One of the distinctive aspects of transition-metal and lanthanide chemistry is cluster formation via metal-metal bonding that is characteristic of many of these elements in low oxidation states [1]. The unique structural, chemical, and... 

Quaternary chalcogenides of the type A Ln M X, containing three metal elements from different blocks of the Periodic Table (A is an alkali or alkaline earth metal, Ln is an /-block lanthanide or scandium, M is a p-block main group or a r/-block transition metal, and X is S or Se) are also known [65]. 

Figure 4.2. The Periodic Table special collective names. The informal symbols of these families of elements are A = alkali metals, Ae = alcaline earth metals, Ln = lanthanides R = rare earth metals = Sc + Y + lanthanides, An = actinides, Hal = halogens, Chal = chalcogens,...

The 3rd group of the Periodic Table (the 1st column within the block of the transition elements) contains the metals scandium, yttrium, lanthanum, and actinium. Lanthanum (atomic number 57) may be considered the earliest member of the family of metals, called lanthanides (general symbol Ln), forming, inside the principal transition series, an inner transition series (up to atomic number 71). Scandium and yttrium together with the lanthanides are also called rare earth metals (general symbol R). 

Considering the overall compound formation capability of the various elements of the 13th group we notice a certain number of analogies between them, such as the compound formation with the metals at the left side of the Periodic Table (with the exception of A1 with the alkali metals), including lanthanides and actinides. 

The lanthanide series is composed of metallic elements with similar physical properties, chemical characteristics, and unique structures. These elements are found in period 6, starting at group 3 of the periodic table. The lanthanide series may also be thought of as an extension of the transition elements, but the lanthanide elements are presented in a separate row of period 6 at the bottom of the periodic table. 

Berkelium is a metallic element located in group 11 (IB) of the transuranic subseries of the actinide series. Berkelium is located just below the rare-earth metal terbium in the lanthanide series of the periodic table. Therefore, it has many chemical and physical properties similar to terbium ( Tb). Its isotopes are very reactive and are not found in nature. Only small amounts have been artificially produced in particle accelerators and by alpha and beta decay. 

Symbol Ce atomic number 58 atomic weight 140.115 a rare-earth metal a lanthanide series inner-transition /-block element metaUic radius (alpha form) 1.8247A(CN=12) atomic volume 20.696 cm /mol electronic configuration [Xe]4fi5di6s2 common valence states -i-3 and +4 four stable isotopes Ce-140 and Ce-142 are the two major ones, their percent abundances 88.48% and 11.07%, respectively. Ce—138 (0.25%) and Ce—136(0.193%) are minor isotopes several artificial radioactive isotopes including Ce-144, a major fission product (ti 284.5 days), are known. 

The periodicity of chemical properties arises from filling of successive quantum mechanical shells of electrons. For example, filling of the s,p shells, with capacities of 8 electrons each, and the d shells, which can hold up to 10 electrons, is associated with the main group and transition elements, respectively (Fig. 1.1). Before the advent of quantum theory, two classes of elements were known that seemed not to fit the Mendeleyevian scheme an uncertain number of rare earth elements or lanthanides— metallic elements, discovered throughout the 1800s, that form oxides of... 

Fig. 1. Apparatus for the preparation of ( 5-cyclopentadienyl)lanthanide complexes from the metallic elements. 

RARE-EARTH ELEMENTS AND METALS. Sometimes referred to as the fraternal fifteen," because of similarities in physical and chemical properties, the rare-earth elements actually are not so rare. This is attested by Fig. 1, which shows a dry lake bed in California that alone contains well in excess of one million pounds of two of die elements, neodymium and praseodymium. The world s largest rare earth body and mine near Baotou, Inner Mongolia, China is shown in Fig. 2. It contains 25 million tons of rare earth oxides (about one quarter of the world s human reserves. The term rare arises from the fact that these elements were discovered in scarce materials. The term earth stems from die tact that the elements were first isolated from their ores in the chemical form of oxides and that the old chemical terminology for oxide is earth. The rare-earth elements, also termed Lanthanides, are similar in that they share a valence of 3 and are treated as a separate side branch of the periodic table, much like die Actinides. See also Actinide Contraction Chemical Elements Lanthanide Series and Periodic Table of the Elements. 

Tucked into the periodic table between lanthanum (atomic number 57) and hafnium (atomic number 72) are the lanthanides. In this series of 14 metallic elements, the seven 4/orbitals are progressively filled, as shown in Figure 5.17 (page 185). Following actinium (atomic number 89) is a second series of 14 elements, the actinides, in which the 5f subshell is progressively filled. The lanthanides and actinides together comprise thef-block elements, or inner transition elements. 

The three columns under oxide and under z/r ratio separate the cations into main group elements, transition metals and lanthanides. 

The atomisation enthalpies of the lanthanides as metallic elemental substances exhibit very different trends. From La to Eu, we see a steady decrease, followed by an abrupt increase at Gd. The atomisation enthalpies then decrease (not quite monotonically) to Yb, then increase at Lu. These trends may be rationalised as follows. According to magnetic studies, the lanthanide atoms in the elemental substances have the electronic configurations 6s25d14f" Eu and Yb are exceptions, discussed further below. The band structure is evidently complex and will not be described in detail. The atomisation enthalpy can be broken down for thermochemical purposes into two steps ... 

For transition metals, the lanthanides, and the actinides, no such simple rule exists. If we accept the ions charges as chemical facts, we can still write the empirical formulas for ionic compounds so that the net (overall) charge is zero. If we had Fe2+ and O2-, the compound would require a minimum of one of each of the elements for a neutral formula, FeO, whereas Fe3+ and O2- would have the formula Fe2C>3. 

Catalytic activity in zeolitic materials is strongly influenced by the type of alkali metal cations, and maximum catalytic activity, e.g, in isomerization reactions, is explained by the formation of an imide species EuNH [305]. Synergetic effects were observed in bimetallic supported Si02 which showed considerable hydrogen uptake during hydrogenation reactions [307]. The formation of Ln-NH2, -NH, -N species seemed to be suppressed in the presence of transition metal powders and precipitation of elemental lanthanides is favored [309]. Lanthanide imides were favored as active species in the Ln/AC-mediated cyclization of ethyne and propyne [310]. 

Europium is a metallic element discovered in 1901 in Paris by the French scientist Eugene-Anatole Demarcay. It belongs to a series of elements called lanthanides, or 4f elements, extending from lanthanum (atomic number 57) to lutetium (atomic number 71). These elements have low abundances Europium occurrence in Earth s crust is only 2.1 ppm (parts per million), that is, 2.1 grams (0.07 ounces) per metric ton, and in seawater, its concentration is as low as 4 X 10 8 ppm. 

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. 

Since their isolation in 1991,1 N-heterocyclic carbenes (NHCs) have become ubiquitous in organometallic chemistry. In more recent years investigations into the coordination of NHCs to other elements have expanded, and there are examples of their coordination to elements across the whole periodic table. This report gives an overview of NHC complexes of non-transition metal elements, ranging from the s-block elements, through the p-block and on to the lanthanides. 

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