Terbium electronic configuration

Although rare-earth ions are mosdy trivalent, lanthanides can exist in the divalent or tetravalent state when the electronic configuration is close to the stable empty, half-fUed, or completely fiUed sheUs. Thus samarium, europium, thuUum, and ytterbium can exist as divalent cations in certain environments. On the other hand, tetravalent cerium, praseodymium, and terbium are found, even as oxides where trivalent and tetravalent states often coexist. The stabili2ation of the different valence states for particular rare earths is sometimes used for separation from the other trivalent lanthanides. The chemicals properties of the di- and tetravalent ions are significantly different. 

Berkelium exhibits both the III and IV oxidation states, as would be expected from the oxidation states displayed by its lanthanide counterpart, terbium. Bk(III) is the most stable oxidation state in noncomplex-ing aqueous solution. Bk(IV) is reasonably stable in solution, undoubtedly because of the stabilizing influence of the half-filled Sf7 electronic configuration. Bk(III) and Bk(IV) exist in aqueous solution as the simple hydrated ions Bk3+(aq) and Bk4+(aq), respectively, unless com-plexed by ligands. Bk(III) is green in most mineral acid solutions. Bk(IV) is yellow in HC1 solution and is orange-yellow in H2S04 solution. A discussion of the absorption spectra of berkelium ions in solution can be found in Section IV,C. 

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]. 

The lutetium hahdes (except the fluoride), together with the nitrates, perchlorates, and acetates, are soluble in water. The hydroxide oxide, carbonate, oxalate, and phosphate compotmds are insoluble. Lutetium compounds are all colorless in the solid state and in solution. Due to its closed electronic configuration (4f " ), lutetium has no absorption bands and does not emit radiation. For these reasons it does not have any magnetic or optical importance, see also Cerium Dysprosium Erbium Europium Gadolinium Holmium Lanthanum Neodymium Praseodymium Promethium Samarium Terbium Ytterbium. 

As previously stated, the REEs are often divided into the light rare earth elements (LREEs) and the heavy rare earth elements (HREEs). This definition is based on the electron configuration of each rare earth element. The LREEs are defined as lanthanum, with atomic number 57 to gadolinium, wifli atomic number 64. The HREEs are defined as terbium with atomic number 65 to lutetium with atomic number 71, and also includes yttrium, with atomic number 39. The HREEs differ from the LREEs in that they have paired electrons (clockwise and... 

Terbium (Tb) with electronic configuration of [Xe] 6s 5d 4f is the first 4f-shell element past half-filling. It is the second of the heavy lanthanides (gadolinium being the first). The nominal filling of its 4f shell consists of seven electrons forming a spherically symmetric half-shell and one... 

The electronic configurations 5f or 4f representing the half-filled f shells of curium and gadolinium, have special stability. Thus, tripositive curium and gadolinium, are especially stable. A consequence of this is that the next element in each case readily loses an extra electron through oxidation, so as to obtain the f structure, with the result that terbium and especially berkelium can be readily oxidized from the III to the IV oxidation state. Another manifestation of this is that europium (and to a lesser extent samarium) -just before gadolinium - tends to favor the 4f structure with a more stable than usual II oxidation state. Similarly, the stable f electronic configuration leads to a more stable than usual II oxidation state in ytterbium (and to a lesser extent in thuUum) just before lutetium (whose tripositive ion has the 4f structure). This leads to the prediction that element 102, the next to the last actinide element, will have an observable II oxidation state. 

The table "Electronic Structure of Isolated Atoms," unlike similar tables as usually published, includes some refinements and additions in accordance with work done in recent years in particular the electronic configuration of the terbium atom has been refined. The table also gives the electronic structures proposed for the elements with atomic numbers from 98 to 103. 

A simplistic picture of the situation is to have a relationship between the efifective moments of the f-element materials with the probable ion configuration. In this situation, localized f electrons in the metal would have the same moment as localized f electrons in a compound. The moment would depend on the number of such localized electrons regardless of the particular f-element s chemical form. Thus, the number of localized f electrons in Gd metal is seven (4f with three electrons in a ds conduction band), as it is in Cm metal (Sfconfiguration) there are also seven localized f electrons in both gadolinium and curium sesquioxides. Further, terbium and berkelium dioxides have seven localized f electrons. All six materials should have the same moment based on seven, unpaired free-ion electrons. 

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