Lanthanum, electron configuration

The element lanthanum (atomic number 57) has the electronic configuration... 

Lanthanide elements, 411, 389 contraction, 413 electron configurations, 415 occurrence and preparation, 413 oxidation numbers, 414 properties, 412 Lanthanum... 

The rare earth (RE) ions most commonly used for applications as phosphors, lasers, and amplifiers are the so-called lanthanide ions. Lanthanide ions are formed by ionization of a nnmber of atoms located in periodic table after lanthanum from the cerium atom (atomic number 58), which has an onter electronic configuration 5s 5p 5d 4f 6s, to the ytterbium atom (atomic number 70), with an outer electronic configuration 5s 5p 4f " 6s. These atoms are nsnally incorporated in crystals as divalent or trivalent cations. In trivalent ions 5d, 6s, and some 4f electrons are removed and so (RE) + ions deal with transitions between electronic energy sublevels of the 4f" electroiuc configuration. Divalent lanthanide ions contain one more f electron (for instance, the Eu + ion has the same electronic configuration as the Gd + ion, the next element in the periodic table) but, at variance with trivalent ions, they tand use to show f d interconfigurational optical transitions. This aspect leads to quite different spectroscopic properties between divalent and trivalent ions, and so we will discuss them separately. 

Group 3 of the Periodic Table consists of the elements scandium, yttrium and either lanthanum or lutetium, depending upon the preferred arrangement of the Table. Group 3 elements have the outer electronic configuration ns2 p, and invariably their solution chemistry is that of the + 3 state. In this text, treatment of both La and Lu is carried out in Chapter 8, which deals with the f-block elements. Lanthanum and lutetium represent the first and last members of the lanthanide series. 

The lanthanide elements are the 15 elements from lanthanum to lutetium. Both La and Lu have been included to allow for the different versions of the Periodic Table, some of which position La in Group 3 as the first member of the third transition series and others that place Lu in that position. If Lu is considered to be the first element in the third transition series, all members of that series possess a filled shell 4f14 configuration. The outer electronic configurations of the lanthanide elements are given in Table 8.1. 

ACTINIUM- [CAS 7440-34-8]. Chemical element symbol Ac. at. no. 89. at. wt. 227 (mass number of the most stable isotope), periodic table group 3, classed in the periodic system as a higher homologue of lanthanum. The electronic configuration for actinium is... 

Rare Earth elements (REEs) elements that occur in the periodic table from lanthanum (La) to lutetium (Lu)—have similar chemical and physical properties due to their electronic configurations. 

Lanthanum, the first member of lanthanides has the configuration of 5d)6s2 and next member cerium, has 4fi6s2 while the next element praseodymium has the configuration 4f3 6s2. Although lanthanum itself does not possess any 4/electrons, it is customary to include this element in the series. The electronic configurations of the elements with fully filled (// and half-filled (f7)/-orbitals are relatively more stable. 

La(Mn,Ga)03 (225), and (La,Ba)(Mn,Ti)03 (308). With less than 50% cobalt, trivalent cobalt is diamagnetic Co111 ( 2). Ga3+ and Ti4+ are also diamagnetic. The electronic configuration of Ni111 may also be correlated with the lattice vibrations (quasistatic model). In Figure 60 are shown the ratios c/ /2a for the lanthanum sys-... 

Three places after xenon there follows the remarkable group of the elements of the Rare Earths, because here, beginning with cerium, the Nf or 4f shell (/ — 3, m = —3, —2, —1, o, 1, 2, 3) is filled up. There is thus produced a group of 14 elements from cerium (58) to lutecium (71), which all possess the same electron configuration of the outermost shell as lanthanum and thus also show a great similarity in chemical properties [group of the lanthanides or lanthanons]. 

The lanthanides (and actinides) are those in which the 4f (and 5f) orbitals are gradually filled. At lanthanum, the 5d subshell is lower in energy than 4f, so lanthanum has the electron configuration [Xe] 6s 5d (Table 2.1). 

Lanthanide elements (referred to as Ln) have atomic numbers that range from 57 to 71. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). With the inclusion of scandium (Sc) and yttrium (Y), which are in the same subgroup, this total of 17 elements are referred to as the rare earth elements (RE). They are similar in some aspects but very different in many others. Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the consequential effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1-5]. 

A t the time of Alfred Werner s birth, the only lanthanide elements that had been identified positively were lanthanum and cerium. Yttrium, a lanthanide element by all criteria except electronic configuration, was known also. However, in 1891 when Werner proposed the substance of the coordination theory, all of the elements of the lanthanide series except promethium, europium, and lutetium had been clearly identified and quite well characterized. Only promethium remained undiscovered at the time of Werner s demise. 

The formation and properties of the lanthanide complex species can be best understood by summarizing first some of the pertinent general characteristics of these elements. In their ground states, the lanthanide atoms have the characteristic valence-shell electronic configurations 4/"5 d 6 or 4 / + 6 where n = 0 for lanthanum and 14 for lutetium, overlying the closed-shell xenon arrangement. The atoms are large and readily oxidized. In both aqueous or nonaqueous systems and the solid state, oxidation... 

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